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. ~.~;.: .. /~_y ~~:~i\~'E.,Stll'. f .AJ..M~~sro.w t~.an1. JMl KARST GEOMORPHOLOGY OF THE PUK.ETOI RANGE, NORTHERN VAIRARAPA, NEV ZEALAND . A thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Geography at Massey Uni versity . Stuart Lorris Halliday December 1987 REFER.ENCE ONL.Y ,. Frontpiece Puketoi Range looking sout h f r om Tr i g 15. The Yaewaepa Range is to the right. Note t he ch2nges i n dr a i11 age texture with res pec t to geology. ii 1--------------------------------------------------------- I I I I I l '' ['o sit on: rccR~; to mus~ o'er Jfoo6 anb }.ff; ! ! [o sfol.l)f ~ truce. ~~ Jorc=-1 s ssu6~ scene; ! ! ,~r~c.rc il3ings t~aI OLL1Il rro1 marr's 6omi.ni.orr bwc.ff; ! : 30n6 mod a[ Joe! ~al~ ru:'er or ra.rd~ been; ! l ~o dim& iC.e, 1rue.kk~s mountain a(f uI15ccn.; l I ll~ I : \iiilq lsc ll'il~ Jfock 1~ru nc.Dcr nc.c6s a Jcf6; l ! ~~orr~ o·ci s!c~ps arr~_joamirrg fuffs lo [corr; I l ~ ~1s 1s not sohtu6c; 115 .out lo ~of 6 ! I [ormcrsc wil~ )bah.trc'5 c~arms; an6 viclD ~er stores urrroff'6." I I I I I I ~ofcn.so 1554.. : I I I I 1------------------------------------------------------------' iii ABSTRACT The research described in this thesis is the first investigation of the karst geomorphology of Pliocene and Pleistocene limestones in the southern Bawke's Bay - northern Vairarapa area. The study area is the Puketoi Range, which is situated 30 km southeast of Dannevirke. The geology of the range is examined and a new geological map of the area has been completed. The Te Aute Group (Pliocene in age) forms much of the range. This consists of two limestone beds, the Te Onepu and Awapapa Limestone Formations interbedded between two mudstone beds. This is overlain by younger Pleistocene material, the Kumeroa Formation, the upper portion of which is limestone underlain by mudstone. Solutional processes and erosion within the range is investigated. Three distinctive types of water are identified: ~llogenic water derived from non-karst areas, autogenic water derived from the limestone, and mixed allogenic-autogenic water. Each of these water types has specific characteristics. The solutional erosion rate for a limestone basin within the range is approximately 58.2 m3 /km 2 /yr. Selected karst and non-karst landforms and features developed on the Puketoi Range are examined. Two of these features, case-hardened limestone and bogaz, have not previously been described in detail in New Zealand. Hany of the features are the result of, or have been modified by, past periglacial climatic conditions. Other landforms are developing under present climatic conditions. The characteristics of three drainage mudstone and greywacke respectively, density on mudstone is the highest of basins developed are investigated. the three basins densities on limestone and greywacke are similar. on limestone, The drainage examined, and Sediment is examined from two caves in the area. Within Ramsay's Neck Cave ancient sediment was probably deposited during the Otira Glaciation. This sediment consists of ancient cave stream sediment, forming basal gravels overlain by fine-grained sediment and, in places, speleothems. This sediment contains allophane, a volcanically derived material, which was possibly deposited after a heavy volcanic ash fall within the cave's iv drainage basin. The sediment examined within PT17 Cave is contemporary gravel fluctuating in response to present hydrological conditions within the cave. Surface features indicate that in the past, gravel has completely infilled the cave, re-establishing surface drainage until the gravel was flushed from the cave. The development of the Puketoi Range cuesta and its subsequent modification is examined. The two limestone beds on which the range has developed strongly control the shape and form of the range. V ACKNOVLEDGMENTS I would like to thank the following people for their help and assistance in the course of my research: I am particularly grateful to Dr Mike Shepherd for his supervision, encouragement and assistance in the field, and for his constructive criticism in the preparation of this thesis. Thanks to Dr John McArthur and Hr Richard Beerdegen, and other staff of the Geography Department, for their help. Thanks also to Dr R.D.Reeves, Chemistry Department, for help with the use of equipment in the analysis of water samples; Dr R.B.Stewart, Ms Jo Thomkins and other staff of the Soil Science Department for their help in the analysis of cave sediment. I am grateful to Dr Ashley Cody, NZGS Rotorua, for examination of the moonmilk sample. I thank Mr Russell Burn, Coonoor, for accommodation, vehicles and assistance during fieldwork; Mr Richard Brown and other farmers along the Puketoi Range for allowing unlimited access to their properties. Thanks to Peter Entwistle, Sue Cade, Jeff Archer, and other cavers for the many hours spent looking for caves and help in their survey; Manawatu Speleological Group for the use of their aerial mosaic photos of the Puketoi Range, and the New Zealand Speleological Society for the grant to help with research expenses. I am indebted to Mr Brian Solomon and Mr David Feek for technical assistance; Mrs Anne Stoddart for help with figures and Mrs Karen Puklowski for help with cartography. Much thanks also to my Hum. I dedicate this thesis to my late Dad for all his encouragement. Also much thanks to Jacqui Aimers for the many days spent in the field, for proof-reading this thesis, help with drawing figures, painting the geology maps, and for all her tolerance and encouragement during the writting of this thesis. FRONT PIECE VERSE ABSTRACT ACKNOVLEDGHENTS TABLE OF CONTENTS LIST OF APPENDICES LIST OF FIGURES LIST OF TABLES LIST OF PHOTOGRAPHS 1 INTRODUCTION 1.1 Introduction 1.2 Aims and Approach 1.3 Study Area 1.4 Natural and Human 1.5 Regional Climate 1.6 Soils TABLE OF CONTENTS History 1.7 Periglacial Climate 2 GEOLOGY 2.1 Introduction 2.2 Previous Geological York 2.3 Economic Geology 2.4 Structural and Tectonic Frame~ork of the East Coast, ii iii V vi ix X xi xii 1 1 2 2 3 7 9 9 12 12 12 14 vi North Island 17 2.5 Palaeogeography and Depositional History of the East Coast of the North Island 21 2.6 Tectonic and Depositional History of the Puketoi Range 26 2.7 Geology of the Puketoi Range 28 2.7.1 Structure 28 2.7.2 Lithology 29 2.7.3 Petrology of Te Aute Group Limestone, Puketoi Range 29 2.8 Geology Hap of the Puketoi Range 30 2.8.1 Method of Geological Investigation 30 3 KARST SOLlITIONAL PROCESSES AND EROSION 34 3.1 Introduction 3.1.1 The Chemistry of Solution 3.2 Method of Investigation 3.2.1 Description of Vater Sample Sites 3.2.2 Results 3.2.2.1 Allogenic Vater 3.2.2.2 Autogenic Vater 3.2.2.3 Mixed Allogenic-autogenic 3.3 Calculation of Solutional Erosion 3.3.1 Computational Techniques in the Estimation of Solutional Erosion 3.3.2 Description of the Towai Drainage Basin 3.3.3 Estimation of Solutional Erosion 3.3.4 Net Rate of Solutional Erosion 3.3.5 Comparison of Solutional Erosion Rate With Other 34 35 37 38 42 43 44 45 46 vii 47 49 49 54 Estimates in New Zealand and World-wide 55 3.4 Conclusions 56 4 KARST LANDFORMS AND CASE-HARDENING WITHIN THE PUKETOI RANGE 57 4.1 Introduction 57 4.2 Fluvial Karst Features of the Puketoi Range 57 4.2.1 Gorges 57 4.2.2 Blind Valleys 58 4.2.3 Steepheads and Pocket Valleys 59 4.2.4 Karst Windows 59 4.2.5 Dry Valleys 59 4.2.5.1 Dry Valley Formation 60 4.2.5.2 Asymmetrical Dry Valley Shape 61 4.3 Dolines 63 4.3.1 Dolines Vithin the Puketoi Range 65 4.4 Karren and Limestone Pavements 66 4.4.1 Karren 66 4.4.1.1 Karren Types in the Puketoi Range 68 4.4.2 Limestone Pavements 70 4.5 Bogaz 72 4.5.1 Terminology 74 4.5.2 Bogaz Vithin the Puketoi Range 76 4.5.2.1 Description of Bogaz at Oporae 81 4.5.2.2 Description of Bogaz at Vaewaepa 82 viii 4.5.2.3 Formation of Bogaz Within the Puketoi Range 82 4.6 Case-hardening of Limestone 84 4.6.1 Previous Studies 84 4.6.2 Case-hardening in the Puketoi Range 86 4.6.2.1 Method of Investigation 86 4.6 . 2.2 Results 86 4.6.2.3 Discussion 87 4.7 Conclusions 89 5 DRAINAGE CHARACTERISTICS 91 5.1 Introduction 91 5.1.1 Surface Drainage - a Generalized View 91 5.2 Drainage Basin Characteristics 92 5.2.1 Method 93 5.2.2 Results 97 5.2.3 Conclusion 98 6 CAVE SEDIMENT 100 6.1 Introduction 100 6.1 . 1 Description of Caves Inves tigated in the Puketoi Range 102 6.1.1.1 Ramsay's Neck Cave 102 6 . 1.1.2 PT17 Cave 104 6.2 Chemical Deposits 6.2 . 1 Speleothem Development 6.2.2 Uranium-series Dating of Speleothems 6.2.3 Speleothems Removed for Dating 6.2.3.1 Description of Samples 6.2.4 Dates of the Speleothem Samples Removed 6.3 elastic Deposits 6.3.1 Description of Clastic Sediment From Ramsay's Neck 104 108 108 109 110 112 112 Cave 112 6.3.1.1 Ancient Cave Stream Sediment 115 6.3.1.2 Fine-grained Sediment 116 6.3.1.3 Analysis of Fine-grained Sediment 117 6.3.1.4 Contempory Cave and Surface Stream Sediment 118 6.3.1.S Discussion of Sediment Size in Ramsay's Neck Cave 119 6.3.2 Gravel Fluctuations in PT17 Cave 120 6.3.2.1 Surface Evidence of Previous Gravel Levels within PT17 Cave 6.3.2.2 Contemporary Gravel Fluctuations within PT17 Cave 6.4 Organic Deposits 6.5 Sedimentation within Ramsay's Neck Cave 6.6 Conclusions 7 CUESTA DEVELOPMENT 7.1 Introduction 7.2 Development of the Puketoi Range Cuesta 7.3 Drainage Development 7.4 Hass Movement and Gravity-sliding on the Scarp Slope 7.5 The Significance of the Limestone Beds within the Puketoi Range 7.6 Conclusions 8 CONCLUSIONS APPENDICES REFERENCES LIST OF APPENDICES 1 PLANTS OF THE ORIGINAL FOREST OF THE "FORTY MILE BUSH" AREA 120 121 124 127 130 132 132 133 135 137 139 140 141 146 206 AND SUBFOSSIL BONES FROM CAVES WITHIN THE PUKETOI RANGE 146 2 LITHOSTRATIGRAPHY OF THE PUKETOI RANGE 150 3 STRATIGRAPHIC SECTIONS OF THE PLIOCENE TE AUTE GROUP IN THE PUKETOI RANGE 158 4 DATA COLLECTED FROM THE ANALYSIS OF YATER SAMPLES 167 5 GRAPHS OF VARIATION IN CARBONATE CONTENT OF YATER SAMPLES AT EACH SAMPLING SITE 176 6 STATISTICAL DATA AND CORRELATION MATRICES FOR YATER SAMPLING SITES 192 7 THORIUM/URANIUM DATING METHOD 198 8 PARTICLE SIZE ANALYSIS OF SEDIMENT FROM RAMSAY'S NECK CAVE AND THE STREAM FLOWING INTO THE CAVE 200 9 POLLEN EXTRACTION METHOD 204 ix X LIST OF FIGURES 1.1 Location map of study area and towns mentioned in the text 4 1.2 Place names mentioned in the text 5 1.3 Graph of variation in rainfall distribution over the Puketoi Range 8 2.1 A map and block diagran illustrating a plate tectonic interpretation of the structure and landforms of Hawke's Bay 18 2.2 Palaeogeographic maps showing development of Hawke's Bay and 'Jairarapa a Pliocene 23 b Early Pleistocene 23 c Middle Pleistocene 24 d Late Pleistocene 24 3,1 Water sampling sites and rainfall collection points in the Puketoi Range 39 3.2 Towai drainage basin 50 3.3 3-D computer dravn image of Towai drainage basin 51 4.1 Hap of asymmetrical dry valleys in the vinicity of Pori 62 4.2 Joint orientation of grikes and bogaz 73 4.3 Location map of bogaz and dolines at Oporae 77 4.4 Location map of bogaz and dolines at 'Jaewaepa 78 4.5 Plan and cross-section of bogaz at Oporae 79 4.6 Plan and cross-section of bogaz at Vaewaepa 80 4.7 Fault patterns in adjoining anticlines and synclines in southeast Algeria 83 4.8 Profile of R-values of case-hardened limestone at Oporae 88 5.1 Hudstone drainage basin on the eastern scarp slope _of the Puket"oi Range 95 5.2 Greyvacke drainage basin on the eastern flanks of the Vaewaepa Range 5.3 Limestone drainage basin to the north of Coonoor, Puketoi Range. 6.1 Ramsay's Neck Cave 96 96 103 6.2 Geology and drainage of Ramsay's Neck Cave and surrounding area 6.3 PT17 Cave 6.4 Sketch of speleothem removed from Ramsay's Neck Cave for dating 6.5 Generalized sedimentary section from passage B, Ramsay's 105 106 111 Neck Cave 113 6.6 Graph of particle size analysis for cave and surface sediment associated with Ramsay's Neck Cave 114 6.7 Relationship between velocities of erosion, transportion, and sedimentation according to Hjulstrom 1935 116 A.l Isopach map (in metres) of the Te Aute Group in southern Bawke's Bay. BACK POCKET Geology Hap of the Puketoi Range LIST OF TABLES 2.1 Tabulation of stratigraphic nomenclature used by previous 152 authors in the Hawke's Bay and northern Yairarapa. 15 2.2 Late Cenozoic chronostratigraphic divisions. 16 3.1 Type of water sampled at each site 43 3.2 Veather data used in the estimation of evaporation 53 5.1 Drainage density figures for three basins in the Puketoi Range 97 6.1 Sedimentary sequence in passage B, Ramsay's Neck Cave, with related cave environmental conditions 112 6.2 Folk-Yard statistics of mean and stanard devjation of cave and surface stream sediments 115 6.3 Analysis of fine-grained sediment from Ramsay's Neck Cave 117 xi xii LIST OF PHOTOGRAPHS FACING PAGE FRONTPIECE Puketoi range from Trig 15 looking to the south. 4.1 Blind valley, Famous Five Cave 4.2 Karst window, Famous Five Cave system 4.3 Beheaded dry valley 4.4 Map of asymmetrical dry valleys in the vicinity of Pori 4.5 Large solutional doline at Coonoor i 58 58 61 61 64 4.6 Subjacent doline 64 4.7 Solutional dolines coalsecing into one large doline 66 4 .8 The same dolines as shown in photo 4.7, but during summer 66 4.9 Karren field on the western side of Oporae 68 4.10 Large rinnenkarren, rundkarren and meanderkarren 69 4.11 Rinnenkarren and rundkarren on nearly vertical rock outcrop 69 4.12 Kamenitzas or cup karren 69 4.13 Cave karren within PT17 Cave 69 4.14 Karrren developed on Hangatoro Mudstone 69 4 . 15 Limestone pavement 71 4.16 View of Oporae bogaz. Photo is looking to the north 4.17 Individual bogaz, southern end of Oporae bogaz area 4.18 Individual bogaz, \laewaepa Station 4.19 Case-hardened limestone at Oporae 4.20 Case-hardened isolated rock 5.1 Drainage basin developed on Mangatoro Mudstone Formation along the eastern scarp slope of the Puketoi Range . 81 81 82 87 87 94 6.1 Phreatic tube and vadose notch within Ramsay's Neck Cave 104 6.2 Longitudinal section of speleothem column removed from passage A, Ramsay's Neck Cave 110 6.3 Cross-section of spelethem removed from passage B, Ramsay's Neck Cave 110 6.4 Speleothem flowstone removed from Alans Ego Chamber, PT17 Cave 111 6.5 Sedimentary sequence -examined ·within Ramsay's Neck Cave 113 6.6 Abandoned stream bed and terraces downstream of PT17 Cave 120 6.7 Gravel level within PT17 Cave before flooding 122 'r. 6.8 Gravel level within PT17 Cave after flooding 7.1 Aerial oblique view along the Puketoi Range, looking towards the south xiii 122 135 7.2 Stream gap behind Hakuri 136 7.3 Large scale mass movement on the southeastern side of Oporae 138 7.3 Gravity-sliding at the southern end of the Puketoi Range 138 CHAPTER ONE INTRODUCTION 1 The investigation of karst areas is a relatively new field of geomorphological and hydrological study in New Zealand. Karst is defined as: "terrain with distinctive landforms and drainage arising from greater rock solubility in natural waters than elsewhere" (Jennings 1985, p.1). The majority of research work into karst areas in New Zealand has been carried out from the late 1960's onwards, with only spasmodic investigations before this time. Thompson (1854, cited in Gunn 1978) produced the first written account of karst terrain in New Zealand and recorded the approximate position and appearance of caves in the Yaitomo district. A review of New Zealand karst literature since this time is given in Gunn (1978). Carbonate rocks are found throughout New Zealand (Horgan 1919; Yillett 1965), ranging in age from Cambrian limestone in the Cobb Valley, north of Nelson, to semi-consolidated Holocene sands in Northland (Gunn 1978; Yilliams 1982a). Karst terrain does not develop on all carbonate rock. The prerequisites for karstification (relatively pure hard rock, high rainfall, and high local relief) must be met before karst features will develop. The most well known areas of karst in New Zealand are the King Country of the west central North Island (Oligocene limestone), the Punakaiki and Paturau districts on the northwest coast of the South Island (Oligocene limestone) and in the Owen and Arthur Ranges to the west of Nelson (Ordovician marble). This thesis examines part of the Kahurangi karst, an area of karst developed on relatively young (Pliocene to Pleistocene) limestone on the East Coast of the North Island (Yilliams 1982a). The area of specific interest is the Puketoi Range. The limestone of this range forms part of a semi-continuous outcropping of thin alternating limestone beds along the East Coast, from northern Hawke's Bay to northern Yairarapa. No detailed geomorphological investigations of the karst in this area had previously been undertaken. Also, all previous investigations in karst geomorphology in New Zealand have been in areas of more massive limestone. For these reasons, the scope of this thesis has not been restricted to one particular area of study within karst geomorphology, but has attempted to give a broad coverage of many aspects of this and 2 associated research fields. 1.2 Aims and Approach The specific aims of this research are: (1) To map, in detail, the geology of the Puketoi Range, emphasising the extent, nature and distribution of limestone beds in the area. (2) To describe the subaerial processes and landforms of karst, and non-karst areas along and near the Puketoi Range. Emphasis is placed on the solutional erosion of limestone compared with mechanical erosion of the area surrounding the range. (3) To discuss subterranean processes and morphologies of the karst area of the Puketoi Range. (4) To explain the evolution of the Puketoi Range: alternating limestone beds. an area with thin In chapter 2, the tectonic history and palaeogeography of the East Coast and Puketoi Range are discussed. The chapter includes descriptions of the stratigraphy, lithology and petrology of the range and a discussion of the new geological map drawn for the area. Chapter 3 is a discussion of karst processes, in particular the spatial and temporal variation in solutional erosion, and the estimated solutional erosion rate of a limestone basin in the area. This is followed in chapter 4 by an examination of karst landforms of the range. In chapter 5, drainage characteristics on differing lithologies in the area surrounding the Puketoi Range are described. Chapter 6 includes a description and discussion of cave sediment and its significance in the geomorphological investigation of the range. Chapter 7 discusses cuesta development and the geomorphological evolution. 1. 3 Study Area There are numerous discontinuous outcrops of Pliocene and younger limestone along much of the East Coast of the North Island, from northern 3 Hawke's Bay to northern Yairarapa. The study area is confined to the Puketoi Range, and the eastern flanks of the Yaewaepa Range, where beds of limestone are exposed. The Puketoi Range is situated approximately 20 km southsoutheast of Dannevirke and extends southward to approximately 16 km east of Eketahuna (see Fig. 1.1). The range is approximately 45 km long and varies in width from 2 km to 5 km (Fig. 1.2). The northern boundary of the study area is taken to be the Vaitahora Valley Road (Grid Ref. U24/830916). (Note - Grid references, unless otherwise stated, are from the NZHS 260 map series. If not, the map series will be given before the grid reference.) The southern limit of the study area is where the limestone of the range thins out, that is, to the south of Pori (Grid Ref. T25/550595). The area is bounded on the eastern side by the steep scarp slope of the Puketoi Range, and on the west by the greywacke of the Vaewaepa Range, and mudstones of Opoitian age. 1.4 Natural and Human History At the time of the arrival of the first Europeans, the Puketoi and Yaewaepa Ranges were covered by dense forest, fern, and swamp vegetation forming part of the much more extensive 'Forty Hile Bush'. The Bush extended from Hauriceville, in the south, to Voodville in the north (Carle 1980). Before forest clearance for farmland, there was a great diversity of forest tree species and forest birds. Giant totara, rimu and rata were common (Carle 1980). Gnarled rata and totara stumps of huge girth are still common in the area due to the wood of these trees being highly resistant to decay. Evidence of the historical diversity of bird-life is seen today in the wide variety of subfossil bird bones found within the caves of the region. Remains have also been found of frogs, snails, tuataras and the extinct moa (Halliday and Gudex 1984). Lists of historical botanical species, and subfossil remains identified in the area are included in Appendix One. There was little Maori occupation of the area, probably due to its harshness and isolation. Evidence of their presence is therefore scant, apart from the existence of a route through the Makuri Gorge to the East Coast, which the present road now follows, and the discovery a number of years ago of a burial cave in the vicinity of Coonoor (S.Macintyre pers. comm.). 4 N r D Woouvil le • Dannevirke Palmerston North• ~ / / STUDY AREA Eketahuna• / / "Mauriceville WELLINGTO~ 0 50 100 150 kilometres Figure 1.1 Location map of study area and towns mentioned in the text. N Pah,a tua Ak Pcinc•a ,to -" roa Road ~ ,_.~,..~ / ( ' "'"" Wa,tahora Mangatoro M.Jl.. <1 11 0 Road Puketoi R oad 5 Road 0 _ __.__JL__kik1~1o;;;m;;-;e~tr;-;;e:;----sl 5 ___ ~ to ---~- · Place Figure 1 2 names ment . 1oned in the text. 5 6 The first European settlement was in 1863 when Captain G.D.Hamilton began farming 12 600 ha of relatively clear country in the Mangatoro Valley (Vilson 1976; MAF Advisary Services Division, Dannevirke 1979). In 1883 Parliament gave 10 OOO pounds for the opening up of Crown Lands in the area (Carle 1980). This resulted in plans for the establishment of the township of Hakuri in 1885 (opened in July 1887), with the first sections offered for sale in February 1892 (Bagnall 1976). The area is a natural break in the range and had once been a resting place for Maori parties travelling from coast to coast (Carle 1980) . The continuous demand for farm land resulted in the gazetting of the area for Special Settlement Association purposes from 1892 onwards. The land was divided into blocks averaging 200 acres (81 ha) with a maximum size of 320 acres (130 ha) (Carle 1980). By the summer of 1892 - 93 the first tracks had been cut into the district, these later being widened into dray roads . This resulted in the rapid influx of settlers, with the associated forest clearance, and early establishment of successful pastoral farming. By 1900 the present pattern of sheep and dairy farming was vell established (MAF Advisory Services Division, Dannevirke 1979). Today the western slope of the Puketoi Range, and the eastern flanks of the Vaewaepa Range, are covered with introduced grasses (with small areas of regenerating forest) supporting sheep, cattle and goats. Farm properties range from 300 ha to 1000 ha, with a few large stations greater than 1000 ha. Stocking rates vary from 8 to 15 stock units per hectare, with Rommeys being the predominant sheep breed and cattle making up 10 to 30 percent of total stock units on most sheep and beef farms (HAF Advisory Service Division, Dannevirke 1979). The development of shafts and other karst features has caused serious problems to farmers. Stock losses down shafts have been estimated as high as 15 percent (pers. comm., Vaewaepa Station). This has resulted in many farmers using explosives and bulldozers in attempts to eliminate such hazards to stock. The eastern scarp slope of the Puketoi Range has little agricultural potential due to the steepness of the land and is covered predominantly in regenerating forest. 7 1.5 Regional Climate The Puketoi Range has mild summers and autumns but is cool in winter and spring. Rainfall is high and reasonably evenly spread, but its effectiveness is reduced by strong westerly winds in spring and late autumn. Local wind patterns in the southern Hawke's Bay - northern Vairarapa region are strongly influenced by the shape of the land. Cook Strait, and to a lesser extent the Hanawatu Gorge, funnel low-level air-streams from the Tasman Sea around the Tararua and Ruahine Ranges and into the region (Coulter 1969). The winds tend to be either westnorthwesterlies through the Manawatu Gorge, southwesterlies east of the Tararua and Ruahine Ranges, or northwesterlies near Cook Strait (Coulter 1969). The Puketoi Range forms a barrier to southerlies and easterlies, sheltering inland districts to the west (MAF Advisory Services Division, Dannevirke 1979) but the range funnels westerly winds, which may reach gale force (up to 150 km/h) during the equinoxes (Noble 1985). These winds have been termed the 'Puketoi gale' and may last several days. The northwesterly facing dip-slope exposed to these westerly winds experiences wide seasonal variations in soil moisture, while the southeasterly scarp is subjected to far less moisture variation due to its sheltered position (Noble 1985). The rainfall and climatological data given below is based on information from the New Zealand Meteorological Service rainfall and climatological stations: D06501 Tataramoa, Makuri (Grid Ref. T25/644700) - record 1943 - 84; D06322 Vaitohora (Grid Ref. U24/830917) - record 1959 - 84; and D06212 Dannevirke (Grid Ref. U23/746062) - record 1953 - 80. The rainfall record for Coonoor (Grid Ref. U24/738808) is based on Mr. Stuart Haclntyre's daily rainfall record, 1956 - 86, read at approximately 8.00 am each day. The average yearly rainfall varies over the Puketoi Range, from a maximum of 2010 mm at Coonoor (480 m a.s.l.), to 1600 mm at Makuri (274 ma.s.l.) and 1278 mm at Vaitahora (250 m a.s.l.) (see Fig. 1.3). There is, on average, 224 days of rainfall greater than 1.0 mm per day at Coonoor (61 percent of days per year), varying from a maximum average of 23 days of mm ?'10 220 200 180 160 140 12 0 \ \ ' \ I 100 ' \ / / .... .... / \ .... / ' I I '-80 \ / - -..., 60 40 ,,. / -- ,, __ ,, ---.,' -----,,. \ ,' ', I \ I \ I \ ,' /" \ I /....._ \ I' I / ........... '------ I \ I ' I.. \ I / '\. ' 1 · \ I / ', I \ \ " ' / I ' ,,, ,,. / / / --. - \ \ ', ' \ ,, I \ I \ I I 20 J F M A M Key . -- Coonoor (Hccord 1956 - 19851 ----Makuri (Record 19'13- 19841 - - Waitahora (Record 1959- 19841 J . J A s 0 N Mo11ths Source · (0011001 - Mr S Macl11tyre. Coonoor Makuri P. V\'aitahora - NZ Met Service D 8 n-, ... , 240 220 200 180 160 140 120 100 eo 60 40 20 Figure 1.3 Graph of variation in rainfall distribution over Range. the Puketoi 9 rain in July (average of 223 mm) to a minimum of 13 days in February (average of 103 mm). About a third of the annual rainfall is in winter (June, July and August). The climatological station at Dannevirke (207 m a.s.l.), the closest station to the study area, records an average yearly rainfall of 1093 mm. The mean annual temperature is 12.3 degrees Celsius, with an average daily maximum of 16.8 degrees Celsius, and an average daily minimum of 7.8 degrees Celsius. The Dannevirke climatological station averages approximately 59 days of ground frost per year and receives an average of 1754 hours of sunshine annually. The Puketoi Range, and hill country down to an altitude of 450 m, are covered by snow three to four times a year, but snow cover usually lasts only two to three days. 1.6 Soils Soils developed in the Puketoi range in many situations reflect the parent material on which they have developed. This has resulted in much of the Puketoi Range, and eastern flanks of the Vaewaepa Range, being covered by Pukeokahu steepland soils (New Zealand Land Inventory Worksheets Nl50, Nl52, Nl54), rendzina soils formed from calcareous rocks with either limestone, or calcareous sandstone and mudstone as the parent material. Gibbs (1980) describes rendzina soils in New Zealand as having either a black, or very dark, greyish-brown A horizon, with a strongly developed granular or nutty structure. Sometimes there may be a brown B horizon between the A horizon and disintegrating limestone rock. Soils developed on non-calcareous parent material in the vicinity of the Puketoi Range generally reflect the nature of the underlying rock, with different soils developed on the greywacke, sandstone and mudstone surrounding the calcareous rocks of the Puketoi Range. 1.7 Periglacial Climate Variations in climatic conditions during the Quaternary have influenced the morphology of many New Zealand regions. Some areas have been heavily glaciated in the past . In the North Island, evidence of previous glacial 10 advances can be seen on the central volcanic area and there is evidence of minor glaciation in the Tararua Range (Yillett 1950). Vithin the Puketoi Range, the effects of past colder conditions have not been as dramatic as witnessed in the glaciated areas, but the present landscape of the range does show evidence of a past periglacial environment. A periglacial environment is primarily influenced oscillations in landform development (Tricart 1968). by freeze-thaw The Otira Glaciation started 70 OOO years B.P., and continued through to approximately 13 OOO years B.P. (Salinger 1984). During this period there were four major glacial advances and three interstadials. The largest glacial advances in the Late Otiran were between 27 OOO and 19 OOO years B.P.. Palaeo-snow-line and pollen evidence indicate a temperature depression of 4 to 5 degrees Celsius below present-day values during this period (Chinn 1983; HcGlone 1983). This period of cooler climatic conditions was followed by a period of warming. The beginning of the Aranuian (c. 13 OOO B.P. to present) saw rapid glacial retreat, and ice diminishing to volumes close to that of present-day, by 12 OOO B.P. (Chinn 1983). Minor glaciation of the lower North Island was first noted by Adkin (1912) from evidence in the Tararua Range, particularly Park Valley (Grid Ref S25/140475). Yillett (1950) estimated a 6 degree Celsius lowering in temperature during the Pleistocene to allow for neve ice accumulation on the Tararua Range. He estimated the composite snow-line to be 1198 m lower than present. This estimate puts the snowline 200 m to 400 m lower than most modern workers' estimates (Chinn 1983; HcGlone 1983). The present highest point of the Puketoi Range is 803 m, 398 m below Yillett's (1950) estimate of the Pleistocene snowline, and 600 m to 800 m below more modern workers' estimates (Chinn 1983; McGlone 1983). This would nevertheless have resulted in periglacial and near-periglacial climatic conditions over much of the Puketoi Range. Villett (1950) believes that the type of forest presently covering the Tararua Range would have survived only on the present coastal flats of the west coast during the Otira Glaciation. On the Puketoi Range, during the same period, the vegetation cover would therefore have been montane to alpine. Neef (1967, 1984) was the first to find evidence within the Puketoi Range of previous cooler phases during the solifluction deposits (resulting from 11 Pleistocene. He observed soil and regolith saturated with water from summer thaw moving downhill as a soggy mass over the frozen ground beneath (Bloom 1978)) in the hill country near Pori. Here tongues of solifluction material were deposited up to 6 m thick and flowed for as much as 1.5 km down Kaitawa Creek and Hirinakitu Stream, on the western side of the range. These solifluction deposits contain blocks of limestone up to 1.5 m in length. Streams have subsequently entrenched their courses, through the solifluction material, to the approximate level of the original stream courses (Neef 1967). Further evidence for the effects of a periglacial climate in the study area will be given in Chapter Four. 2.1 Introduction CHAPTER TYO GEOLOGY 12 In an area such as the Puketoi Range, the relationship between geomorphological processes and landform development cannot be fully understood without a knowledge of the geological structure and lithology. However, possibly owing to the isolated and exposed nature of the Puketoi Range, and its position on the boundary of the provinces of Bawke's Bay and Vairarapa, there is a lack of comprehensive geological investigations covering the range as a whole. Many of the previous geological studies of the area (see below for more detailed references) have been restricted to the individual provinces, resulting in a lack of continuity in the classification and nomenclature of geological beds within range. After a careful study of all published geological literature of the area, it was recognised that confusion and inaccuracy could only be avoided by the production of a new geological map, incorporating the entire range, which would enable the data of previous workers to be assessed and correlated. For this reason, the production of a geological map became one of the major objectives of this thesis. The following chapter has been divided into two sections. The describes the structure and tectonic setting of the East Coast. followed by a discussion of the palaeogeography of the area. The first This is second section, which is largely based on field studies, examines the structure, lithology and petrology of the geological beds comprising the Puketoi Range. This section concludes with a description of the stratigraphy and a new geological map of the range (see back pocket). 2.2 Previous Geological Vork The earliest reference to geological investigation of the southern Bawke's Bay - Vairarapa area appears in Hochstetter (1864, cited in Lillie 1953). Later Hochstetter, in his "New Zealand" (1867), gave a "synoptical view of geological formations and strata" and described the "Bawke's Bay series", as " .•. a group of limestones, sandstones and clay marls, replete with fossils belonging to the latest Tertiary Formations" 13 (p.61).Some of the fossils described are from the Te Aute Group fauna (Lillie 1953). Crawford (1870) investigated the area when it was still in thick virgin forest and made the first geological description of the Puketoi Range. He states: "I found the blue clay, (which he had found throughout the district) and on the ridges above, Tertiary sandstone beds, with the usual fossil shells" (Crawford 1870, p.349). In 1877 Hector described the geology of the eastern district of the lower North Island, inland from Castlepoint, and including the Puketoi Range. He noted a succession of clay marls and limestones forming the range. McKay traversed the country between Cape Kidnappers and Cape Turnagain. He produced the first geological sketch map, on a scale of 1:50 OOO, and proposed the first stratigraphic classification of eighteen different beds comprising the Cretaceous and Tertiary strata (McKay 1877a, 1877b). Of the eighteen beds he proposed, the original classification of several formations has been retained to the present day. Henderson in 1915 drew attention to the prominent Mangatuna Fault, which is located at the contact between the greywacke of the Yaewaepa Range and the limestone of the Puketoi Range. Ongley (1935) mapped the 4400 square kilometre Eketahuna Subdivision, publishing a geological map on the scale of 1:253 440. He outlined the approximate distribution of the post Opotian strata of which the Puketoi Range forms a part. Neef (1967, 1984) considers this as particularly accurate where Ongley found well defined lithological changes. Lillie (1953) mapped strata in the Dannevirke Subdivision, describing the Mangatoro, Te Aute and Kumeroa Formations on which the Puketoi Range has developed. This work, and that of Kingma (1971) on the Te Aute Subdivision, is incorporated in the 1:250 OOO Dannevirke sheet (Kingma 1962). Laing (1963) described and mapped the Yaipatiki area (NZHS 3 NlS0/5). This encompasses the northern end of the Puketoi Range, that is, the area around Oporae (Grid Ref. 024/824875) identifying three formations: Oporae (Opoitian to Mangapanian in age), Totara Road Limestone (Mangapanian), and Kumeroa (Nukumaruan). 14 Neef (1967, 1974, 1984) described and mapped the Eketahuna District. This includes the southern end of the Puketoi Range, from approximately Hakuri south, where he describes the Hakuri group. This consists of sandstones, siltstones and limestones, Yaipipian to Nukumaruan in age. Beu et al. (1980) mapped the distribution of Cenozoic limestones, from northern Hawke's Bay to northern Yairarapa, and correlated limestone facies within a biostratigraphic framework. Harmsen (1984a, 1984b) described Pliocene temperate shallow marine sediments in southern Hawke's Bay, dividing the Te Aute Group into six formations, four of which outcrop in the Puketoi Range. More detailed reference will be made to the work of Lillie (1953), Neef (1967, 1974, 1984), Beu et al. (1980), and Harmsen (1984a, 1984b), later in this chapter. The stratigraphy which the above authors have used within the Hawke's Bay - northern Yairarapa region, is listed in Table 2.1 . Absolute ages for the New Zealand series and stages, referred to in Table 2.1, and their relationship to international subdivisions of geological time, are provided in Table 2.2. Numerous other authors have made passing reference to the southern Hawke's Bay - northern Yairarapa region, in the vicinity of the Puketoi Range, many in relation to potential reservoir rocks for hydrocarbon accumulations and the limestone resources for agricultural lime. No modern studies have covered in detail the geology of the Puketoi Range as a whole. The lack of detailed geological maps and stratigraphic sections, and the non-uniform nomenclature may have deterred geomorphological studies. 2.3 Economic Geology The analysis and distribution of limestone for sutiable agricultural use, in the southern Hawke's Bay - northern Yairarapa region, have been described (for example Aston 1915a, 1915b, 1918; Morgan 1919; Lillie 1953; Kitt 1962; and Moore and Belliss 1979). Pliocene limestones are presently quarried for agricultural lime in four major quarries in the central and southern Bawke's Bay, with a total production of 230 OOO tonnes in 1971 (Moore and Belliss 1979). Limestone is also quarried for McKAY 1187 ONGLEY 1135 Lilli( 1953 LAING 1983 NHF 196 7 19" ,n• KINGMA 1971 Cen1n1 I Ellellhua Denn••"'' W11o,et 11L1 Area E\.tt1hun1 Subd1w111on Te Aull 5',t,d1v111on tOUlhtrn SubdP1111on Subd nt11 ,on H•wUI II• Uoo, , ,n,, l 1m111a,,1 KUfflt,OI 1Cum1,01 ,.,.,... 5,,. •• 11011 5.,""11ont t un,u Formation Fo,m111on Uoo,, Mtllur, s,11,,on• L • "'' 11on1 fac•• .. > towtr ,0,1 l11'1ttton• f .. Te Autt LIS1 To10,e "o•d D " Tt Ault Sh•I JI'"' S t l"IO I IOllt . Tt Ault L1m111on1 . . "' Lo•• ' Mtkvtt S,IU IOf'I SdtllO"' fOtfflll t Of' > MU:utt .. fe AuH . :I Ooo,tt SanOt tont '0'"'"'·" ~ v ,o,,.,•• ••" s.,. •• T1n1 .. > 0 ..; SenOelOl"II ....... ,.,o,o .___,_ • C Fotm1t1D'1 > C . . .. S1vl"ldl'I ... S,11,tol"lt Mef'OIOUIII Fo,m1t1on Table 2.1 Tabulation of stratigraphic nomenclature authors in Havke's Bay and northern Vairarapa. ,,, ... . ; • .! ManQatOtO fo,rnet,ol"I used by BEV 01 II 1910 HA~MS(N 118• ltlS THIS TH(SIS N(W l(ALAN O G1tt10,n1 I H1w1Lt1 C tf'ltr1I I 1outhern "''•to, llll1n9• STAGlS a .. H1w1111 It¥ l/$ l(u~tN or ltvffl l fOI lUl'ft l fOI NUl(UMAJIUAN ,,,,,., Jorm11t0n ,.,,,,., (otm111on For"'• ' ,on M/S l'or I L1m111on• Te On1ou r. Ono•:~ Tt Ault l1mettont l,.1fflltlOl"II L ,,..,,,o,.., MANGA,AHl•N . . u llll1u-.1w1 lllltulltwl MudtlOf"II Mvdttont . C 0 . Te a.tat1 l ,,...e11on• AwaD•O• Aw10•0• wa1,i,1AN ~ Wf'le talt "" l 11"\ee1on• l 1""'9110n• I •'"•"one ~ ~ -..01100••• S 1ndeton• . ; • . h""'",~ ~ ~1ua1t•u l,mello"• .. l 1m•lfOl"I ~ ~ 0 " " ... ,,-0110,0 ... ,..,,.,o,o Of"OIT IAN . . , Fo,m1t,ol"I ; fo,,.,,1,on • • :. . ~ KA" Tl AN previous ~ (J1 16 Ser ies S1age Aye of International bounda')' D ivisions lMal HAWERA HOLOCENE .. . - .. - . ... - - -- - ··- ·-··. 0 35 w z w u CASTLECLIFFIAN 05 0 ~ 11 U) w NUKUMARUAN I 85 _, WANGANUI . C Cl. c20 w MANGAPANIAN z · C 2 3 w WAIPIPIAN u 32 0 OPOITIAN :J 50 Cl. --- ··· ... KAPITEAN .. . TARANAKI { · · c60 MIOCENE TONGAPORUTUAN Table 2.2 Late Cenozoic chronostratigraphic divisions. Time in millions of years (Ma) and correlative international divisions. (From Neef 1984) roading, for use in concrete products, and for building purposes, while large blocks are used for river bank and foreshore protection work. Some of the particularly pure limestone is used in glass manufacture (Kingma 1971). The largest quarry in the Puketoi Range is the Makuri Gorge Quarry (Grid Ref. T25/609689). Analysis of this limestone gave purities between 88.8 percent and 96.0 percent (Moore and Belliss 1979). Aston's (1915b) analysis of elements in the limestone gave the following results: CaC0 3 93.3 percent, insolubles 4.6 percent, Al/Fe oxides 1.3 percent, and MgC0 3 0.8 percent. Average yearly production from the quarry for agricultural use, between 1973 and 1977, was 2876 tonnes (Moore and Belliss 1979). Since the 1940's much of the East Coast of the North Island has been prospected for oil. The Pliocene limestones are potential reservoir 17 rocks for hydrocarbon accumulations. As well as having high porosity and permeability values, the limestones are transgressive and diachronous. This increases their hydrocarbon potential due to possible entrapment of oil, and/or gas, beneath an upper unconformity (Forder 1975). Small oil and gas seeps have been known since late last century throughout the East Coast, particularly in the Gisborne area, but no economic accumulations of oil have been found (Leslie and Hollingsworth 1972). A review of the hydrocarbon potential of the area was made by the Petroleum Corporation of New Zealand (Exploration) Ltd, in 1978 (cited in Harmsen 1984a). The Pliocene limestone was found to be freshwater saturated from the examination of wells drilled in the southern part of the East Coast Basin. This indicates that these potential reservoirs have been extensively flushed and can no longer be considered to have significant petroleum potential . 2.4 Structural and Tectonic Framework of the East Coast, North Island The boundary between the Pacific and Indian plates passes along the eastern margin of the North Island (Yalcott 1978; Cole and Lewis 1981; Davey et al. 1986) forming a 500 km elongated depression known as the Hikurangi Trough. The oceanic crust of the Pacific Plate is subducted obliquely beneath continential crust of the Indian Plate, to form the Taupo-Hikurangi arc-trench system, (Fig. 2.1). This extends from the Hikurangi Trough, on the eastern side, to the Taupo Volcanic Zone on the western side. The relative motion between the two plates varies from almost normal to the plate boundary, in the northern part of the North Island, to almost transcurrent in the south of the North Island (Davey et el. 1986). For approximately 200 km west of the Hikurangi Trough, the Benioff Zone dips beneath the accretionary prism. The prism is up to 150 km wide and characterized by a series of imbricate thrust faults, along which movement becomes progressively more oblique (dextral) towards the west. On the outer eastern edge of the prism is the accretionary slope, comprised of a series of ridges and basins 5 km to 30 km wide and 10 km to 60 km long (Lewis 1980). Sediments on the accretionary slope are ptogressively older westwards, away from the Hikurangi Trough, with the Highest accretionary Taupo Volcanic Zone Forearc basin ridge Accret1onary slope H1kurang1 Trough I _1mm/vr- Figure 2.1 A map and block diagram illustrating a plate tectonic interpretation of the structure and landforms . of llauke's Bay. Fine stipple represents continental crust. Lines represent faults, mostly thrust faults. Solid diamonds represent andesite-dacite arc. Open domes represent rhyolite and pantellerite volcanoes. Open diamond represents Egmont high-K andeslte volcano. Inverted V Indicates possible volcanic knolls. The map Is from Cole and Leuis (1981) and the cross-section from Kamp (1982). 18 19 older sediments forming the higher accretionary ridges, for example, the Puketoi Range. The inner part the highest sediments. The of the prism is structurally a forearc basin (also termed accretionary basin) filled by thick Plio-Pleistocene sediments are crossed by strike-slip faults which increase in number and displacement westward (Cole 1984). The prism is bound on the west by a frontal ridge composed of upper Palaeozoic-Mesozoic greywackes and argillites, as seen in the Ruahine Range. This ridge is undergoing rapid uplift. Present uplift rates are estimated to vary from 2 m to 7 m per 1000 years along the axis of the ranges (Wellman 1967). Studies of marine terrace surfaces at the southern end of the North Island , give uplift rates of 3.0 m to 4.5 m per 1000 years (Ghani 1978). The volcanic component of the Taupo-Hikurangi arc-trench system is the Taupo Volcanic Zone (Healy 1962) which extends northnortheast from Ohakune to White Island, and comprises a main andesitic arc. In the remainder of this section the accretionary prism, and in particular, the highest accretionary ridge and the accretionary slope will be considered in more detail. Uplift of the ridge and offshore slope has resulted in the exposure, at the surface, of a semi-continuous outcrop of limestone along the East Coast of the North Island, part of which forms the Puketoi Range. Along the East Coast of the North Island three clearly separate topographical landform units are recognised in relation to the accretionary prism system: (1) The North Island axial range; including the Tararua, Ruahine, and Kaweka Ranges; in the west representing the frontal ridge. These ranges are composed of strongly deformed and uplifted Mesozoic greywacke. (2) The East Coast Inland Depression which represents the highest accretionary basin, extending from Cook Strait to Hawke Bay, which is interrupted only by northern Vairarapa a basement high area in the vicinity of Ht. Bruce, (Bruce Hill No. 2 Grid Ref. !25/329479). The depression is made up of sunken late Pliocene to Pleistocene sediments. (3) The East Coast Uplands, which represent the higher accretionary 20 ridges (together termed the "highest accretionary ridge" by Walcott 1978). This is a 30 km to 40 km wide belt of hilly country which separates the inland depression from the Pacific Ocean, and includes several minor ranges such as the Puketoi Range. The area is composed of highly deformed Cretaceous and Tertiary mudstones and limestones. This then extends down the accretionary slope to the Hikurangi Trough. The accretionary prism, with its basin and ridge system, is the result of landward-thinning wedges of sediment being scraped from the surface of the subducting plate, as it is forced underneath the feather edge of the over-riding plate (Lewis 1980) (Fig. 2.1). As each new ridge is accreted, older wedges, with active thrust-faults between them, are pushed upwards, and landwards, and rotated towards the vertical. This forms the accretionary slope, with each wedge forming a topographic ridge that dams sediment to landward in an accretionary slope basin. The imbricate stack of wedges, particularly the highest accretionary ridge, form a major trench-flank ridge which creates the eastern margin of a relatively large highest accretionary basin. The highest accretionary ridge from Hawke's Bay south to Uruti Point, southern Wairarapa, has a progression of seaward-faulted, or sharply dipping, anticlinal ridges (Lewis 1973; Katz 1974) and flat-floored, sediment filled synclinal basins, aligned more or less parallel to the slope (Fantin 1963; Lewis 1976). This extends seaward down the accretionary slope to the Hikurangi Trough. The basins range from 5 km to 30 km wide (ridge to ridge crest), and 10 km to 60 km long (Lewis 1980). Strata in the basins are thickest at their landward limit, varying from 200 m to 2000 m thick (Lewis 1980), and then wedge out towards the seaward anticline ridge tops. The oldest beds in any basin dip most steeply landward, and it is inferred from this that they have been tilted from the original, near-horizontal inclination, of the younger overlying beds (Lewis 1980) .. Sedimentation changes, related to interglacial sea level highs, and glacial sea level lows, are thought to have produced unconformities within the Quaternary strata deposited on the accretionary slope (Lewis 1971, 1973). Lewis (1980) believes these unconformities can be tentatively correlated with dated maximum glacial extensions. On the basis of these correlations Lewis (1971) estimates the rate of uplift on 21 the coastal hills to range up to 1.7 m per 1000 years. He estimates the rates of subsidence in the shelf basins to range up to 1.5 m per 1000 years, with rates of tilting reaching a maximum of about 0.03 degrees per 1000 years. Analysis of deep water foraminiferal faunas, from sediment cores of some upper slope anticlines, show uplift of at least 1000 m since Pliocene times (Lewis 1974). Present uplift rates along the Hawke's Bay coastline have been estimated by Berryman (cited in Kamp 1982) at 2 m per 1000 years. Uplift along the southern \lairarapa coastline is estimated at 1. 7 m to 2.2 m per 1000 years at Oterei (Singh 1971). Uplift rates at the \iThite Rocks vary from O. 75 m to 4.0 m per 1000 years, for the growing anticlines, and subsidence rates at 0.5 m to 2.2 m per 1000 years, for the growing synclines (Ghani 1978). There is substantial sediment supply to the accretionary slope owing to the proximity of the eroding frontal ridge mountain system, the rising coastal hills, and showers of ash from volcanic activity. This continuous supply of material has filled the basins, and in some places draped over growing anticlinal ridges (Lewis 1980). The area of maximum sedimentation varies in relation to the sea level at the time of deposition, with the most rapid zone of deposition migrating back and forth as sea level varies in response to the waxing and waning of ice sheets. As sediment is deposited most rapidly in a coast-parallel prism (Lewis 1973), this prism will move in response to sea level changes. The prism is at present formed on the accretionary slope, ranging from 4 km to 10 km from the coastline, where water depth ranges from 30 m to 100 m. Sedimentation rates are estimated to range from 1.5 m to 3.0 m per 1000 years (Lewis 1980) with present sedimentation being rapid and muddy (Lewis 1980). 2.5 Palaeogeography and Depositional History of the East Coast of the North Island During the late Miocene and early Pliocene the sea covered an extensive planed surface of Mesozoic greywacke basement rocks over the East Coast area. In Kapitian time, the \langanui - Hawke's Bay seaway extended as far south as Eketuhuna depositing mud in that area and shallow water 22 sediments further north (Beu et al. 1980). Deposition of the Te Aute Group strata began during the early Pliocene with the formation of the northeast-southwest trending fault-controlled depression, along the boundary between the Indian and Pacific plates. The depression was deepest around Hawke Bay; the greatest depth was approximately 500 m before the early Pliocene, with water depth never more than 100 m after this time (Harmsen 1984a). This depression extended westward across the area now occupied by the Ruahine Range and Vanganui Basin. This is based on Opoitian sediments on top of the Ruahine Range (Beu et al. 1980). The axis of the basin continued to subside, accumulating thick, monotonous mudstone (Mangatoro Formation) deposits through most of the Pliocene, along the basin axis adjacent to the Ruahine high. The eastern side formed an extensive alternating shallow water carbonates sediments were deposited (Harmsen 1984a). shallow platform on which and deeper water terrigenous This Harmsen believed was the result of large-scale alternations in relative sea level positions. This is accounted for by the tectonic setting of the area, and glacio-eustatic changes in sea level, as first suggested by Vella (1965). These changes in sea level have had a major control in the lithology of the sediments, with widespread simultaneous water depth (Harmsen 1984a). cyclic variations inferred from changing This area was the first to be uplifted, forming the East Coast Uplands. Land was exposed in the early Pliocene to the north of Castlepoint, and by the late Pliocene, this area had extended northwards into Hawke's Bay (Fig. 2.2a), Subsidence in the depression kept pace with sedimentation (3.5 cm per 1000 years) with local variations in the thickness, assumed by Harmsen (1984a) to result from contemporaneous tectonic deformation. During late Opoitian time, marked shoaling is evident in northern and central Hawke's Bay, with the deposition of the Kairakau Limestone and Mokopeka Sandstone Formations. The early Vaipipian was a time of widespread carbonate deposition, with extensive barnacle banks formed along the shallow western margin of the depression (Beu et al. 1980). This is attributed to a glacio-eustatic lowering of the sea level (Beu et al. 1980; Harmsen 1984a). Vaipipian 39·5 40'5 41 '5 175°E A .Pl iocene 176°E 111 ·e £ ,,,_,.;,~;,,,- . 1/.-'.·~'.»;,( - --p-..;-· ~ ... . ·~.Y -..;,.' m~·:::::;~;;,Y-: ...:;,,"> .............. .J ~ :,'/ , ... ,;~--~', ~:.>.~v·::-, ..::::: .;- ~ ~ .•.•,, ·.·• I ::::,,:;." . iC/ f ( -:s;,"'",...J' .fl ..f -;,,,' -~ Kuripap~r Hawktt Bay 5tra,t~o°1:>/ .1('}%7. . .. Cape ns ·e ~ .· /"" ~ '''""""'' Manawatu ;. {§j;~ 51ra11 / ':::--..."'>"' D PI ,ocone sed -<~' .;!fijj. ,nleroed ,mentat,on f,. j~' ~ Late Pl,o c ene 1· \ J .. . ~NS;,->: now uposed ,mestone :• ' 0.,. ,;:: - -/11 />.·. <-~~ . ~ Early Pl1ocene lorn f, , ,,, -., .w ' ~- ""'" "'"' -~ · t-{"1 ~ P lloce ne la nd ,n late PI 1ocene ¥ ' '..':>"> / exposed mudsi one now . ? j ·' ·cast lepo,nt C) ~ ~ . Deep m1rone ,(.J : / .. _. fr_] ~arly · ... ··· ·. :: ~ _.·· ··. La nd 1n earl y PI 1oc ene .,,,/ Inferred shoreline Pre sent shoreline / Oce.1n current Pl1ocene ·. X.~ ... · only, ·. ~ ~ .··· / I • / 0 020 304050km 175'[ 176 ' E 177'E 178'£ 175 'E 17 6'E ,n·e 178'E 39'5 39 ·5 .,_ 40°5 41°5 B . Early Pl eis toc e ne 40'5 .,_ ~1~~:~~~~- ~~'~> 6~~ ~~'-> ~e, /.··- ·. · .• ""'" 1>0-J, / -~. , ~ ·· ~,, .. e ~,' i ' ~.' l(.3...,.,ie. ... ,, --- - t, --·· .::::~:-· • Hawke Bay I I ) ,._ , (V.· , ~ ~ Cape ,t:j ,iJ :,,::,,('~:} Kidnappers ~ .f , t ~' ...... l:/-:~ 5tra~J,j7/~· . .,: j",// ~~ G Moxed elastic & ca lcareous ·J 'f~4Y_--,. ~~~~ sed1m entat1on interred :, . . , <., 'v ,. ~., ,·,. ~~ .' m lnter bedded l1mesto ne & , /:::,. hallol· • "-~'-..:~ · mudstone no w expo sed · C.."<-· rnarin < • 1," '-." : . . .-... :'I, . · .. -~ ....._ / 0 Early Pl e osto ce ne marin e 41· 5 f- .··' -$>,'):~-:::::: .. · _:., J .· ~~,;Castl cpo ,nt claS ll cs now exposed ~ ' De e p . , . -~ D L . ' ~~:<::-~'.'.':'_~_- : · ·; 'h ~-.....:::::_ · • nd 1 ~ early Ple1st ocene ~'(.\~"?(.::-:-:-:-- <:- , .,,: /::::::~ _.,,,, Inferred shor e li n e '" ':-J, _:7:::· .. -::: ~- ·,. ~~ tarly Pleostoce ne ••.· -·· :. ; . :~~ Present shoreline ' . .. -~--C'oo -~· - Ocean currents ,f ~~'" S'rr,,; 1 ~ ~304050km I --'-L.-0 I 175 ·e 176'[ 177'[ 178' E Figure 2.2 \lairarapa. Palaeogeographic maps show ing de velopment of Hawke 's Bay and (a) Pliocene, (b) Early Pleistocene. (Redrawn from Kamp 1982, and Kamp and Vucetich 1982). -I 39'5 -14 0°5 4i'5 N w 39'5 176 °E 177°F C. Middle Pleistocene .· #9,. ~~I • c"'""""' . ~ ~·F ,'i~ .;, / ~ .§•$:i'·~.._o-.. ~'~.~ ~~ :;:2 ~ ,.__--..;r .~o":2° ~y , ~<.,- ~'-."""~~ ~ , J§:2,i.::-:::2' ~ -- ,,- ,~, .... ~·-· -•J~ C'oo ~ ·. '~· +J' _:~· l'r., · ~ Q'/( -:-..~ 175'E 176'E 177'E Palaeogeographic maps (c) Middle Pleistocene • Middle Ple is tocene Urata now e ... posed CSJ Erod,ng hills of Triass ic to early Ple,s tocune strata ,," Interred limit of sedimentation ' 1n m id Ple1s 1ocene Present ,horel1ne 17B'E 39·5 40° 5 41 ·s development of Late Pleistocene. showing (d) Figure 2.2 \lairarapa. Kamp 1982, and Kamp and Vucetich 1982 ). 39'5 Hawke's Bay (Redrawn 175.E and from 176'E 17(,'E 177'E Ila Late Ple1s1ocene · ' strata Cast lcpo ,nt ~ ~~.~ed~~ 1 ~~e\n1eo~e ne strata D Tna ss,c - m1d<11e P l,ocene s lr dta ,./ 125 OOO y r BP shore l ine U°.lfl :l~ km 178 'E 39's 41 ·s N +'> 25 limestone and calcareous sandstone (Awapapa Formation) were deposited from Cape Kidnappers south to Eketahuna. These were deposited in very shallow depths, the limestone being an intertidal and shallow subtidal carbonate deposit. Their high terrigenous content also suggests proximity to the shoreline (Harmsen 1984a). The Vanganui - Hawke's Bay seaway still existed, with Vaipipian limestone cropping out along the Ruahine Range (Browne 1978). Along the present Vaewaepa Range, and elsewhere along the East Coast, where greywacke highs were uplifted, Vaipipian limestones contain large subangular greywacke clasts at their base. This suggests sedimentation adjacent to an emerging greywacke fault block. Coastal hills, from Cape Kidnappers to Cape Palliser, were above sea level by this time, with a major seaway still existing from Hawke's Bay southwards into the Vairarapa, and westward over the emerging Ruahine Range into the Yanganui Basin (Kamp 1982). This constriction and shallowing of the depression, to a depth of 30 m, throughout the Vaipipian time, resulted in large-scale cross-bedding of the shallow bioclastic limestone. The coarse nature of sediment suggests strong tidal current activity (Harmsen 1984a). Vith the earthquake activity recorded in local mass-emplaced deposits and slump units, and the rapid variation in limestone thickness, Harmsen (1984a) believes tectonic deformation was the major external control on sedimentation during this time. In the late Vaipipian, carbonate sedimentation was followed by renewed deposition of terrigenous sand and mud (Raukawa Hudstone), considered by Harmsen (1984a) to have resulted from increased water depth in response to a reduction in global ice volume. Greywacke clasts within Mangapanian (late Pliocene) strata, along the margin of the depression, suggest emergent land to the east (Vaewaepa Range) and west (Ruahine Range) of the depression (Harmsen 1984a). The Vanganui - Hawke's Bay seaway was still present. Sedimentation during this period was initially mud-dominated throughout the area, but shoaling to the north, possibly resulting from tectonic uplift (Beu et al. 1980; Harmsen 1984a), resulted in the deposition of Argyll Sandstone (Harmsen 1984a). This was followed by widespread, mainly mid-shelf (30 m to 60 m), carbonate deposition (Te Onepu Formation), with the formation of large sand waves and sand ridges, under the influence of strong tidal currents (Harmsen 1984a). This is believed by Harmsen (1984a) to have 26 resulted from a relative sea level rise through glacio-eustatic change. The Vanganui - Hawke's Bay seaway still existed in early Nukumaruan time (Beu et al. 1980). The Ruahine Range had been uplifted by this time to form islands in its central part (Fig. 2.2b). the East Coast Increased tectonic activity caused the middle of Depression to sink and the sides to rise (Beu et al. 1980). Uplift of the Mount Bruce Block (Grid Ref. T25/329479) closed the seaway to the south of Hawke's bay after early Nukumaruan time (Vella 1962). Deposition of numerous thin, muddy, shelly limestone beds in central Hawke's Bay probably resulted from glacio-eustatic oscillations in sea level during the Nukumaruan time (Beu et al. 1980), This also occurred to a lesser extent in southern Hawke's Bay, as seen in the lithological changes in the Kumeroa Formation. By the end of the early Pleistocene subsidence of had ceased and the whole area was uplifted above open folding in the Pliocene, changed to more folding early in the Pleistocene, giving way to the inland sea level. widespread reverse and depression The initial and tighter transcurrent faulting later (Kamp 1982), By the middle Pleistocene erosion of the surface was well established, with rivers transporting and depositing sediment, lakes accumulating sediment, and large gravel fans forming along the eastern margin of the Ruahine Range (Kamp 1982) (Fig. 2.2c). Huch of the landscape seen today developed during the late Pleistocene and Holocene periods (Fig. 2.2d). The uplift initiated in the middle Pleistocene continues through to the present, with volcanic activity periodically covering the area with airfall deposits (Kamp 1982). Chapter Seven covers in detail the geomorphological development of the cuesta, and karstic development of the Puketoi Range. 2.6 Tectonic and Depositional History of the Puketoi Range The structural and tectonic framework, and the palaeogeography of the East Coast have been discussed above. specifically on the Puketoi Range. This section will concentrate 27 The Puketoi Range is the highest wedge of Tertiary sediment, forming part of the accretionary ridge system, uplifted by the subduction of the Pacific Plate beneath the Indian Plate. This wedge of sediment has been pushed upwards, and landwards, by the movements of the plates (Lewis 1980). Basement greywacke on the feather edge of the Indian Plate has been deformed in the process of subduction of the Pacific Plate. This has resulted in the basement high of greywacke, of the Puketoi Range) being uplifted between system in the east, and the forearc basin the Vaewaepa Range (west the accretionary ridge in the west. Tertiary sediments have been eroded off the Vaewaepa Range to expose the underlying greywacke. The rapid uplift of this range has influenced the pattern of sedimentation in the basin formed between this range and the Puketoi Range. The proto-Puketoi Range developed as a sharply dipping anticlinal ridge which has subsequently been eroded to leave the limestone-capped dip slope on the western flank of the anticline. The original anticlinal form of the Puketoi Range is seen today in the many sharply dipping anticlinal ridges formed on the accretionary slope (Lewis 1973; Katz 1974). Calcareous material from current-swept and sediment-free anticlinal ridges was deposited in adjacent basins and on the flanks of the anticlines (Kamp 1982). Deposition tended to be thicker in the centre of the basins, thinning towards the top of the anticline ridge. This pattern of limestone deposition has strongly influenced the shape of the Puketoi Range. The evolution of the range began with the deposition of sediment from late Miocene time onwards. The main stratigraphic group, the Te Aute Group, began forming in the early Pliocene and continued through to the late Pliocene. By early Vaipipian time, the area which became the Puketoi Range was near sea level, with limestones and calcareous sandstones deposited. The Vaewaepa Range had been uplifted above sea level, with erosion of the range supplying sediment to the basin. By mid Vaipipian time the area to the east of the Puketoi Range had also been uplifted and was beginning to erode. This resulted in the constriction and shallowing of a seaway between this eastern uplifted land and the Ruahine Range, with the Vaewaepa Range forming an island between the two. Sedimentation in the area which formed the Puketoi 28 Range continued, with the deposition of alternating calcareous and non-calcareous deposits related to changes in sea level caused by either glacio-eustatic changes or tectonic uplift. Sedimentation continued through to Nukumaruan time, when uplift of the Mount Bruce basement high closed the seaway. The area of the Puketoi Range rose above sea level in the early Pleistocene. Subsequent uplift and subaerial erosion has resulted in the landscape of the range seen today. 2.7 Geology of the Puketoi Range In the following section, the geology of the Puketoi Range will be discussed. This is based on previously published work (Lillie 1953; Neef 1967, 1974, 1984; Harmsen 1984a, 1984b, 1985) and field work carried out by the author. 2.7.1 Structure Structurally, the Puketoi Range may be termed a cuesta, consisting of a gently dipping west-facing slope, covered predominantly by the Te Onepu Limestone Formation, and an eastern steeply dipping scarp slope, formed on a succession of geological beds, particularly the Folding and faulting of these geological beds Alfredton-Makuri-Hangatuna fault runs the length of Hangatoro Formation. has occurred. The the Puketoi Range. In the northern section the fault forms a distinctive boundary separating the greywacke of the Vaewaepa Range, from the Te Aute Group and Kumeroa Formation deposits of the Puketoi Range and eastern flank of the Vaewaepa Range. Neef (1967, 1974, 1984) also identified many minor faults at the southern end of the range. Large-scale and small-scale synclinal and anticlinal folding has occurred in the geological beds of the Puketoi Range. The range originally developed with the formation of a large asymmetrical anticline, on which a series of smaller synclines and anticlines have developed. This is clearly seen in the northern section of the Puketoi Range where a series of anticlinal and synclinal folds have formed (see cross-section A-A', back pocket). 29 The basin formed between the Puketoi and Vaewaepa Range has been infilled with younger marine sediments, accumulating the Kumeroa Formation sediment during the Pleistocene. These sediments have formed adjacent to the Vaewaepa Range as it was being uplifted. Eroded greywacke pebbles are found in the beds. The deposit has also been faulted and folded . 2 . 7.2 Lithology Late Miocene to Pleistocene sediments were deposited in the location of the present Puketoi Range, and on the flanks of the emerging Vaewaepa Range . These sediments are characterised by thin, 20 m to 70 m thick, alternating beds of barnacle-rich coquina limestone and calcareous sandstone. These are interbedded between 60 m to 240 m thick, terrigenous deposits of siltstone and mudstone , which are occasionally sandy or carbonaceous (Harmsen 1984a, 1984b, 1985). Rapid vertical and lateral facies changes are also characteristic of the geological beds of the range. This results in a great variation of thickness and continuity of the beds. For example, the Raukawa Formation varies in thickness from 60 m, at Coonoor (Grid Ref . U24/784827 - 773833), to 40 mat Hakuri (Grid Ref. T25/690671 - 680682). The lithology of individual formations is given , in detail, in Appendix Two. The description of the Te Aute Group is based on the work of Harmsen (1984a, 1984b, 1985), while that of the Kumeroa Formation is from Lillie (1953). 2.7.3 Petrology of Te Aute Group Limestone, Puketoi Range Sweeting (1978) examined the petrology of the limestone of the Puketoi Range. At this time, the published geological map of the area showed the whole of the range to be Te Aute Group deposits. From the map drawn by the author, Kumeroa Formation is identified in the area Sweeting examined. Therefore, some of her samples may have been Kumeroa Formation limestone and not Te Aute Group limestone as shown on Kingma's (1962) map. From the eight to ten limestone specimens she examined, Sweeting made the following comments: "This is a very fossiliferous rock, all organisms closely packed together and although fragmental their margins are generally smooth and rounded and appear to have been transported over a prolonged period of aeposition. The matrix in which these fossils are embedded is very fine and like them appears to have been laid down under very quiet conditions. Scattered through the rock are clean bright quartz fragments, some showing distinct prismatic outlines. The rock is clean and fresh and there are no evidences of any alteration products." (Sweeting 1978, p.254) 30 Sweeting estimated the effective porosity of the limestone as between 5 and 12 percent, with insoluble residue determined at 5 to 10 percent. All of the insoluble residue was quartz. Sweeting also made the following general observation of the New Zealand Tertiary limestones, to which the Te Aute Group belongs. The limestone showed no recrystallisation, in the specimens she examined, though they were quite hard and lithified. She found calcite occuring as cloudy or smudgy patchs full of inclusions and fragments, and rarely occurring in rhombic or platey forms. She found no true micrites or sparites, the limestones mainly consisting of biomicrites and biosparites, with a fairly high porosity. The texture was fine to medium. The quartz grains were large fractured grains and stout prismatic crystals and there were a few pyramidal sections, which occurred chiefly in clear allotrimorphic forms with no inclusive material (Sweeting 1978). 2.8 Geological Map of the Puketoi Range Geological mapping of the Puketoi Range has, in the past, been restricted to either generalized coverage of the area, for example Kingma's (1962) work, or detailed geological investigation of only a small portion of the range, for example Neef's (1974) investigation. This lack of detailed geological information for the range as a whole restricts any geomorphological investigation of structure/landform relationships and it was for this reason detailed mapping of the range was undertaken by the author. 2.8.1 Method of geological investigation Geological information used in the drawing of the map was obtained 31 primarily from fieldwork and aerial photograph interpretation, with additional information information was placed N.150/5, 7, 8; N.153 / 6; from previously published material. This onto aerial mosaic maps (N . Z.H.S. 3 Sheets and N.154/ 1, 4) at a scale of 1:15 840. The information was then transferred and reduced to a scale of 1:63 360, and finally to a scale of 1:50 OOO. The area mapped is covered by the metric maps N.Z .H.S. 260 U24, U25, T24, and T25 . Approximately four weeks was spent in the field investigating the geology of the range, with the area north of Coonoor receiving the greatest attention, owing to its geological complexity. The southern part of the range mapped by Neef (1967, 1974, 1984), was given a reconnaissance check to correlate his stratigraphic nomenclature with that of Harmsen (1984a, 1984b, 1985), and to confirm the position of beds described by Neef (1974). Huch of the central part of the range was not field checked, either because of its isolated nature, or the simplicity of the geology as indicated by aerial photograph interpretation. Aerial photographs at a scale of approximately 1: 25 OOO were used in conjunction with a stereoscope, to give a three dimensional image of the area. The photograph runs used were: SN 5139 G/ 26-30; SN 5139 H/ 31-35; SN 5139 I / 30-33; SN 5310 A/ 10-15; SN 5310 B/ 7-13; SN 5310 C/ 5-9; SN 5408 G/ 16-18; and SN 5408 F/ 18. The photographic coverage included most of the range, and enabled the identification of geological beds . The nomenclature used for the identification of the geological beds is 1985). The three based on the work of Harmsen (1984a, 1984b, stratigraphic columns described by Harmsen (1984b) are used as the basis for stratigraphic (Appendix Three) . used (Neef 1967, positioning of the geological beds along the range Neef's work on the southern end of the range was also 1974, 1984). Faults and folds identified by Neef were transferred directly correlated with the on to the map. work of Harmsen, Geological or adjusted boundaries were when found to be incorrectly placed . The position of the greywacke of the Waewaepa Range is based on Lillie (1953) and Kingma (1962). Position and naming of all the faults, anticlines and synclines are based on previous work. The Mangatuna fault was first recognised by Henderson 32 (1915). Other faults shown are described by Neef (1967, 1974, 1984). The synclines and anticlines shown are from the work of Laing (1963), Ridd (1964), and de Caen and Darley (1969), for the area north of Hakuri, and from Neef (1967, 1974, 1984) for the area south of this. The Oporae anticline may possibly be more correctly termed a monocline, with the east facing beds dipping very gently. Dips are based on the author's fieldwork, Neef (1974), and Lillie (1953), with each indicated differently on the map. The geological cross-sections shown at the bottom of the map are based on the results of the author's fieldwork and Neef (1974) (cross-section C-C'). They illustrate the close relationship between structure, lithology and landforms which will be examined later in chapters Four and Seven of this thesis. Geological boundaries shown on the map identified by fieldwork or interpreted indicate lithological changes from aerial photographs; for example, the pronounced lithological change from the Te Onepu Limestone Formation to the underlying Raukawa Hudstone Formation. Further refinement of the map may be possible with detailed palaeontological studies. For the overlying instance, the boundary between the Te Onepu Formation and Kumeroa Formation cannot, in places, be accurately identified on the basis of lithology alone. An accurate geological map of the Puketoi Range was required by the author before geomorphological investigations could be made. Other than the work of Neef (1967, 1974, 1984) on the southern end of the Puketoi Range, there was no detailed geological information available before the drawing of this geological map. Huch of the previously published geological information about the Puketoi Range is very generalized or contains considerable inaccuracy. Kingma (1962, 1967), for example mapped the Puketoi Range on the basis of the age of the geological beds and not on lithological variation within the beds. This resulted in the majority of the range being mapped as Yaitotaran and Opoitian in age, with only generalized lithological variation within each stage given. Inaccuracy in the interpretation of the structure of the range has also occurred. This is seen in the work of Beu et al (1980) who estimated the thickness of the limestone within the range to be 200 m from a traverse 33 from Coonoor to the top of the range (Grid Ref. U24/797825-778918). This is considerably greater than the thickness which Harmsen (1984a, 1984b, 1985) estimated to be 20 m (for the Te Onepu Limestone Formation) and 40 m (for the Awapapa Limestone Formation) in the same area (Grid Ref. U24/784827-773833). Harmsen's estimates are considered by the author to be far more accurate. 3.1 Introduction CHAPTER THREE SOLUTIONAL PROCESSES AND EROSION 34 The solubility of limestone in natural waters results in the solutional development of karst landforms. The understanding of the solutional processes has greatly increased the understanding of the development of karst landforms. Shaler (1890) was one of the first to propose ideas on the solubility of limestone, suggesting that the amount of C0 2 dissolved in soil water greatly influenced solution. Grund (1903) and Cumings (1906) recognised that carbonic acid was produced by water and C0 2 • The influence that air and water temperature have on the solution of limestone was also recognised at this time (Sawicki 1909). By the 1930 1 s the importance of C0 2 in the solution of limestone was more fully understood (Adams and Swinnerton 1937), and the influence of climate on karst morphogenetic processes and resultant landform assemblages was also appreciated. For example, O.Lehmann in 1927 recognised altitudinal zonation in karst features and in 1936 H.Lehmann, from his work in the tropics, proposed that climate played a dominant role in karst morphogenetic processes. In the early 1950's the influence of biological activity in the production of C0 2 was once again stressed (Schoeller 1950; Trombe 1952; Roques 1956). The influence that the relationship between temperature and C0 2 has on solutional processes was also observed (Birot 1954). Water at a lower temperature can contain more dissolved C0 2 than water at higher temperatures. Corbel (1959) concluded that colder climatic conditions result in more rapid solution than tropical climates. A year later Bogli (1960) argued to the contrary. He proposed that increased temperature resulted in the higher production of organic matter and, -as a result, higher C0 2 concentrations in soil water. As a consequence, he argued that greater amounts of carbonic acid are produced in the humid tropics and subhumid regions. Corbel's work received more attention because of its quantitative nature and also because of the boom in quantitative geomorphology at that time. 35 It was not until later in the 1960's that the effect of variation in temperature on C0 2 production was seen as being less important than C0 2 produced by vegetation. Also during this time, solutional rates and carbonate concentrations within karst areas were found to vary both horizontally and vertically. Villiams (1968, p.1) proposed that solution is irregular in time and place resulting in variations in the spatial and temporal distribution of solution. The importance of partial pressure of C0 2 is now clearly understood, as is the effect of temperature on solution. Geological variations in lithology and structure also influence solution (Sweeting and Sweeting 1969; Jennings 1971) but their effects are still not fully understood. The combined effects of climate, geology, relief, vegetation, soils, and drainage are now seen as being influentual in the solutional processes in individual drainage basins, and the resultant landform development. Over the past 20 to 30 years, many estimates of karst solutional erosion rates have been made. Smith and Atkinson (1976) summarised 134 estimates of the rate of solutional erosion and 231 reports of the hardness of springs and river waters. Vi thin New Zealand, Dowling (1974) and Villiams and Dowling (1979) studied solution of Ordovician marble in northwest Nelson, and more recently Gunn (1978, 1981) estimated solutional erosion of Oligocene limestone in the Vaitomo district. This chapter discusses solutional processes and erosion within the Puketoi Range. This is the first investigation in New Zealand of solutional processes on Pliocene/Pleistocene limestones. The chapter begins with a discussion on the chemistry of solution. This is followed by a description of the method of investigation, and a list of water sampling sites within the Puketoi Range. The characteristics of the water sampled are discussed and an estimation is made of solutional erosion from a small drainage basin at Coonoor. 3.1.1 The Chemistry of Soluti6n The chemistry of limestone solution has been discussed by many researchers. In this section, only a brief discussion is given. For a more detailed account, see for example, Pickett, Bray and Stenner (1976). 36 Many processes operate in the development of karst landscapes, the most important possibly being solution of the limestone by water. The maximum solution of calcite in pure water is 13 mg 1- 1 at 16 degrees Celsius and 15 mg 1- 1 at 25 degrees Celsius (Jennings 1985). This is well below the concentration of calcium and magnesium found in the natural water systems of karst areas, where values commonly range from 200 mg 11 to 250 mg 1- 1 (Trudgill 1985). The higher concentrations of CaC0 3 and HgC0 3, measured from water samples, are due to the increased aggressiveness of the water with the addition of acids, predominantly carbonic acid from dissolved C0 2 • The main source of the C02 is plant root respiration and the bacterial decay of organic matter (Pitty 1966). Other acids, such as humic and sulphuric acids are of importance, but only locally. The solution of CaC03 occurs through a complex series of ionic dissociations and reversible reactions, governed by activity constants and saturation equilibria. The following simplified discussion is taken from Jennings (1985). For a more detailed account, see Picknett (1976). Hydrogen (H+) and hydroxyl (OH-) ions are found in solution, as some water molecules are always in a state of dissociation. These ions react with C02 to form carbonate acid: co 2 * co2 (air) (aq) Co2 +H2o* H2C03 (aq) Both of these reactions proceed slowly. dissociate into its constituent ions. The carbonic acid can also The physical solution of CaC03 also proceeds slowly: CaCO * Ca2+ + CO 2- 3 3 (solid) The following two reactions occur extremely quickly: 37 The amount of limestone dissolved is therefore dependent on the hydrogen ion concentrations, and this in turn is usually dependent on the C0 2 in solution. The quantity of C0 2 held in the water is governed by the water temperature and partial pressure of the carbon dioxide (pC0 2 ) in the air with which the water is in contact (Henry's Law). The temperature effect is an inverse one, with lower temperatures allowing more C0 2 into solution. The more C0 2 there is in the air, the more that can go into solution until an equlibrium is reached. The pC0 2 ranges from 0.03 percent by volume in open air, near sea level; to values of 0.5 to 2 percent in soil and cave air, with extreme values a magnitude higher (Jennings 1985). Solution by acidic water continues until saturation equilibrium is reached between the air, water, and rock. In the open system this may vary from a few hours to a number of days, due to the slow progress of some of the reactions discussed above. In the closed system, which happens when soil water passes down into joints and fissures in the limestone, saturation is reached much sooner but at lower concentrations of CaC0 3 • 3.2 Method of Investigation In order to investigate the spatial and temporal variation of solution in the karst area of the Puketoi Range, and to estimate solutional erosion of a karst drainage basin within the area (see section 3.3), 15 water sampling sites were chosen from within the range. The water examined at these sites was derived from karst areas only, non-karst areas only, and water of mixed origin. Three of these sites (3, 12, and 13) are from a drainage basin at Coonoor where solutional erosion of the range was estimated. This will be discussed later in the chapter. 38 Weekly sampling was carried out from 7.3.86 to 19.8.86, with additional samples collected from sites 3, 12, and 13 on 14.9.86 .. The information about the measurements were recorded each collected, and is given in Appendix Four. The dry bulb and wet bulb air temperatures time a water sample was The date and time was noted. and relative humidity were recorded using a whirling hygrometer. This was spun continuously for approximately two minutes before the readings were taken. The temperature was read to the nearest 0.5 of a degree Fahrenheit. These measurements were converted to the equivalent in degrees Celsius. The relative humidity of the air at the time of the reading was estimated from the chart supplied with the whirling hygrometer. The water temperature was also measured using a thermometer reading to 0.1 degrees Celsius. The thermometer was placed in the water for approximately two minutes before the reading was taken. Yater samples were collected in 100 ml polythene bottles from the surface layers of water from each site. Each bottle was labelled with a site number, and used in the collection of water from only that site. the collection of a sample, the bottle was washed three times water at the site. The sample was then brought back to University, where it was analysed using a Varian techtron Before in the Hassey AA-100 spectrophotometer to measure calcium and magnesium content. The pH was also measured. The analysis of the samples was usually within two to three days of collection, with the period never exceeding six days. 3.2.1 Description of Yater Sample Sites A brief description of each sampling site is given below. This details the grid reference, physical features, and the lithology of the rock at each sampling site. These sites, and the rainfall data collection point are shown on Figure 3.1. SITE 1 Mangatoro Stream (Grid Ref. U24/799927) This site is situated at the northern end of the Puketoi Range, near the approximate northern limit of limestone beds in the range. The samples were collected from beside the bridge, where the Mangatoro Road crosses the Hangatoro Stream. Water at this site is derived from the greywacke N S 1 wat er sampli ng site 1 R r ain da ta co llec tion point 5 0 5 10 k ilom et re s Figure 3.1 ~ater sampling sites and rainfall collection point in the Puketoi Range. 39 40 of the Yaewaepa Range, and the limestones and mudstones of the Puketoi Range. SITE 2 Mangatoro Stream (Grid Ref. U24/762842) Site 2 is upstream from site 1, approximately midway between the headwaters of the stream and site 1. Samples were collected from beside the bridge, where the Mangatoro Road crosses the Mangatoro Stream. At this site water is also derived from the Vaewaepa and Puketoi Ranges. SITE 3 Towai Drainage Basin Resurgence, Mangatoro Stream (Grid Ref. U24/737827) Yater collected from this site is derived from the caves and surface streams which flow from the crest of the Puketoi Range, down through the Famous Five Cave system to resurge at this site (Fig. 3.2). Samples were collected from the drain passing under the Mangatoro Road. Yater samples from this site were used to estimate solutional erosion of limestone within the Puketoi Range. SITE 4 Spring, Mangatoro Stream (Grid Ref. U24/737824) Site 4 is a small spring on the western side of the Mangatoro Stream. Yater examined here is from limestone. Each water sample was collected from the centre of the spring. SITE 5 PT17 Cave Resurgence, Mangatoro Stream (Grid Ref. U24/731820) The true resurgence to the PT17 downstream and 20 m lower than Cave system is approximately 100 m the site sampled. Access to this resurgence is difficult, therefore a higher level overflow resurgence was sampled. Here water flows from two sites between the limestone boulders collapsed over the cave entrance. The water flowing through the cave is derived from the Vaewaepa Range and water percolating through the limestone overlying the cave. Vater samples were collected from the small stream flowing from this resurgence. 41 SITE 6 Stream from the Vaewaepa Range (Grid Ref. 024/724817) Site 6 and Site 7 are streams originating on the greywacke of the Vaewaepa Range. Site 6 is the stream which flows directly into PT17 Cave. The samples were collected from the approximate boundary between the limes tone of the Puketoi Range and the greywacke of the Vaewaepa Range. The sampling site was slightly downstream of the gravel pit. SITE 7 Stream from the Vaewaepa Range (Grid Ref. 024/719812) Samples were collected from the true left stream above the junction with the stream flowing along the boundary of the limestone and greywacke. This site was on the greywacke of the Vaewaepa Range. SITE 8 PT17 Cave, Coonoor (Grid Ref. 024/725814) This, and sites 9, 10, and 11 are from within PT17 Cave (Fig. 6,4) . Yater sampled at these sites is derived from the greyw'acke of the \Jaew'aepa Range and water percolating through the limestone above the cave. Site 8 is at the appearance of a small stream within the cave (1narked as site 8 on Fig. 6.4. Sites 9, 10, and 11 are also marked on this figure). SITE 9 PT17 Cave, Coonoor (Grid Ref. 024/725814) Samples were collected from the bottom of the waterfall within the cave. This stream is the same as that sampled at site six on the surface. SITE 10 PT17 Cave, Coonoor (Grid Ref. 024/725814) This site is situated approximately 5 m downstream from the junction of the two streams ("Record Junction", Fig. 6.4) flowing through the cave, that is, the combined streamflow of water sampled from sites 8 and 9. SITE 11 PT17 Cave, Coonoor (Grid Ref. 024/725814) This site is situated at the downstream end of the cave ("Bottle Neck Squeeze", Fig. 6.4), where the water passes through a narrowing of the passage walls, then travels approximately 20 m downstream before 42 disappearing into a gravel sump. SITE 12 Famous Five Cave Submergence (Grid Ref. 024/741817) This site is situated within collected from the stream as it system (Fig. 3.2). areas only. The water the Towai drainage basin. Samples were submerges into the Famous Five Cave sampled here is derived from limestone SITE 13 Famous Five Cave Resurgence (Grid Ref. 024/740822) This site is also situated within the Towai drainage basin. Samples were collected from the pool at the resurgence of the Famous Fi ve Cave system. This water is also derived from limestone areas only. SITE 14 Makuri River (Grid Ref. T24 / 654704) This site is situated at the bridge below the Makuri village, where the Makuri Owahanga Road crosses the Makuri River. The water sampled at this site is from the Vaewaepa and Puketoi Ranges. SITE FIFTEEN Makuri River (Grid Ref. T25/627688) This site is situated below the bridge, where the Pori Road crosses the Makuri River. This site is the most southern collection site along the Puketoi Range. River height measurements were also taken from the staff positioned on the bridge. The water sampled here is derived from the Waewaepa and Puketoi Ranges. 3.2.2 Results A total of 306 water samples were analysed from the 15 sites within the Puketoi Range. The information obtained from the analysis of the samples is given in Appendices Four, Five, and Six. Three distinctive types of water were identified within the springs, surface streams, and cave streams examined. The three water types are: allogenic water derived from non-karst areas, autogenic water derived from karst areas, and mixed allogenic-autogenic water derived from karst and non-karst areas. The characteristics used in distinguishing of each of these water types will 43 be described below: each site. Table 3.1 indicates the type of water sampled at Table 3.1 Type of water sampled at each site. Allogenic Autogenic Site Number 6, 7 3, 4, 12, 13 3.2.2.1 Allogenic Vater Mixed 1, 2, 5, 8, 9, 10, 11, 14, 15 Allogenic water was identified at sites 6 and 7. This water is derived from the greywacke of the Vaewaepa Range, and has had little or no contact with limestone. The water therefore has a low CaC0 3 content, and the HgC0 3 content is close to the CaC0 3 content. The mean CaC0 3 values for these two sites was 9.02 mg 1- 1 at site 6 and 8.24 mg 1- 1 at site 7. These were the lowest mean CaC0 3 values recorded for the 15 sites investigated. Hean MgC0 3 content of the water samples at both sites (8.36 mg 1- 1 at site 6 and 7.21 at site 7) were very close to the mean CaC0 3 content. On occasions the HgC0 3 content exceeded that of CaC0 3 • For example, on 5.5.86 and again on 11.5.86 the HgC0 3 content was greater than CaC0 3 at site 6. Allogenic water is aggressive to limestone with all samples analysed well below carbonate saturation (Appendix Five). This again reflects the lack of contact with limestone. At most other sampling sites, '