GEOLOGY OF THE RAUKUMARA AREA

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RAUKUMARA AREA

Scale 1:250000

c. MAZENGARB 1. G. SPEDEN (COMPILERS)

Institute of Geological & Nuclear Sciences 1:250000 geological map 6

Institute of Geological & Nuclear Sciences Limited , New Zealand

2000 BiBLIOGRAPHIC REFERENCE

Mazengarb. c.; Speden, I.G. (compilers) 2000: Geology of the Raukumara area. Institute ofGeological & Nuclear Sciences 1:250 000 geological map 6. I sheet + 60 p. Lower HUll, ew Zealand. Institute of Geological & Nucl ear Sciences Limited.

Development and maintenance ofARCIINFO GIS database by D.W. Heron and M.S. Rattenbury

GIS operations by D.W. Heron, l.A. Lyall and l . Arnst

Contributions to offshore geology by PM. Barnes, L. Carter, A. Nicol and C.1. Uruski

Edi ted by D.W. Heron and MJ. Isaac

Prepared for publication by L. Redmond

Printed by Graphic Press & Packaging Ltd, Levin

ISBN 0-478-09708-5

© Copyright Institute of Geological & Nuclear Sciences Limited 2000

FRONT COVER

Hikurangi (1752 m), the highest nonvolcanic mountain in the , towers over the surrounding deeply dissected countryside. Hikurangi is interpreted as an isolated remnant (klippe) of a formerly more extensive thrust sheet of Torlesse rocks, which now overlies slightly younger, Eariy Cretaceous Waitahaia Formation. The high hill to the east (left) is Aorangi (1272 m). Photo CN41042: D.L. Homer CONTENTS

ABSTRACT Q UATERNARY SEDIMENTS 34 Keywords Pl eistocene sedi ments of th e Waipaoa catchment 34 Shall ow marine sediments near 36 INTRODUCTION Marine terraces . 36 Coasta l plain deposits 36 THE QMAP SERIES I All uvial terrace and fl oodplain deposits 36 The QMAP geograph ic inform ati on system I All uvial fa ns . 37 Data sources J Landslides 37 Reliability I Te Pu ia sinter 38

REG IONAL SETTING 3 TECTONIC HISTORy .41

GEOMORPHOLOGY 3 Early and Late Cretaceous .41 Raukulnara Range 3 Late Cretaceous to Oligocene .41 Northern tip of Raukumara Peninsula 3 Miocene to Recent . .41 Eastern foreland 3 Active faulls and folds 42 Offshore ph ysiography and geology 7 GEOLOGICAL RESOURCES ...... 45 STRATIGRAPHY 10 Aggregate 45 LATE JURASSIC TO Groun dwater 45 EA RLY CRETACEOUS BASEMENT 10 Hot springs . .45 Torlesse composite terrane .. 10 Limestone.. . 45 Terrane nomenclatu re 10 Snlectite . 45 Torlesse rocks of the Raukumara area .. II Metall ic minerals . 45 The contact between Torl esse and overl ying rocks . . 15 Oi I and gas . .45

IN-PLACE CRETACEOUS TO ENGINEERING GEOLOGy ...... 47 OLIGOCENE ROC KS 17 Earl y and Late Cretaceous rocks of th e Basement rocks ..47 Matawai Group 17 Cretaceous to O ligocene sedim entary rocks .47 Early and Late Cretaceous rocks of the Matakaoa Volcani cs 47 RuaLori a Group 19 Miocene and Pl iocene rocks .47 Late Cretaceous to Paleocene rocks 20 Quatern ary sediments 47 Eocene and O li gocene rocks 2 1 GEOLOGICAL HAZARDS .48 THE EAST COAST ALLOCHTHON . ... 2 1 Early Cretaceous to Eocene igneoll s rocks.. . 23 Volcanic acUvi ty 48 Earl y and Late Cretaceous sedimentary rocks 23 Erosion 48 Late Cretaceous to Paleocene sedimentary rocks 25 Slope instabil ity and landslides .48 Eocene and Oli gocene sedimentary rocks 26 Seismotectoni c hazard (by M.Stirli ng & C. Mazengarb) 5 1 MIOCENE AND PLIOCENE ROCKS 26 Tsunami 5 1 Early Mi ocene 27 Middle and Late Mi ocene.... 29 AVAfLA BfLlTY OF QMAP DATA 52 Latest Miocene and Pliocene 3 1 Melange 33 ACKNOWLEDGMENTS . 52

REFERENCES ...... 53 INTRODUCTION

THE QMAP SERIES oth er digital data sets, fo r example gravity and magneti c surveys, mineral resources and localities, fossil localities, This geological map of the Raukumara area is the sixth active faults, and petrological samples. The primary of a new national map seri es known as QMAP (Quarter­ soft ware used is ARC/INFO®. Digital topographic data million MAP, Nath an 1993; Fig. I) be ing produced by was obtain ed from EagleTechnology Ltd ., Terralink, and the Institute of Geological & Nuc lear Sciences Ltd. Land Information New Zealand (LLNZ). (GNS). QMAP supersedes the previous 1:250000 ("four miles to the " or '"four mi le") geological maps which The QMAP series and database are based on detailed are now dated (e.g. Ki ngma 1965, 1966). Since these geological information pl otted on the L1 NZ Infomap 260 maps were published new conceptshave been developed, seri es 1:50000 topographic base maps. Thesedata record and th ere has been mu ch detai led onshore and offshore sheets are avai lable for consu ltation at GNS offi ces in geological and geophysical mapping by govern ment, Lower HUll and . The 1:50000 data have been university and industry scientists. The requirement for simplified for digitisi ng during a compilati on stage, with geological information has also in creased as a result of the linework smoothed and geological units amaJgamated the ResQurceManagement Act, greater demands all to conform to a standard national system based on age geological resources, a new educational syllabus and the and lithology. Point data (e.g. stru ctural ) greater public awareness of natural hazards and their have not been simplified. All point data are stored in the mitigation. This map presents a revised interpretation of GIS, but only selected representati ve struc tural the geology, geological hi story and structure of the observations are shown on th e map. Procedures fo r map Raukumara Peninsula and adjacent areas offshore. compi lation and details ofdata storage and manipulation techniques are given by Rattenbury & Heron (1997). The geology of th e Raukumara area is in many places complex and considerable simpl ifi cation has been Data sources necessary to make it appropriate for present ation at 1:250000 scale. Rock un its are mapped primarily in terms The map and text have been compi led from published of their age of deposition, eruption or intrusion. As a maps and papers, unpublished university theses, GNS consequence the colour of the units on th e map face techn ical and map fil es, measured section column files, refl ects their age, with overpri nts used to differentiate mi ning and petroleum expl orati on company reports, field some lithologies. trip guides, th e New Zealand Fossil Record file in its di gital form (FRED) and the GNS Geological Resources Letter symbols (i n upper case, with a lower case prefi x database (GERM). Additional fi e ld mapping was to indicate early, middle or late if appropriate) indicate undertaken to attain a uniform minimum level of coverage the predominant age ofthe rock unit. The last lower case over the map area and to solve problems. However, some letter or letters indicates a fo rma ll y named areas remain unexplored and problems remain. Many of lithostratigraphic unit and/or th e predominant lithology. the landslides and fau lts were mapped from ai r photos, Age subdi vision is in terms of the intern ational time scale. with limited fie ld checkin g. Offshore data have been A time scale diagram showin g correlation between the compiled from a published synlhesis (Field, Uruski et international and local time scales and absolute ages in al. 1997) and from surveys by the National Institute of millions of years (Ma) is shown insi de the front cover Water & Atmospheri c Research Ltd (NIWA). Data (after Crampton et ,,/. 1995 , 2000; Graham et "I. 2000). sources are pl otted on the accompanyin g diagram (Fig. 2) and identi fl ed in the references. The accompanying text is generalised and is not intended to be an exhaustive description of the various rock uni ts Reliability mapped. For more detailed information the reader is referred to work cited througho ut the text and listed in The accuracy with which geological contacts, fau lts and the references. fold s are shown is diminished by the compilation and simplificati on process, and by th e scale of publication. The QMAP geographic information system Point data are accurately located to within 100 m in terms of th e NZMS 260 grid.The unpublished 1:50 000 data The QMAP seri es uses computer methods to store, record maps have a hi gher standard ofdetail and accuracy. manipulate and present geological and topographical The 1:250000 map is of regional scale onl y and should information. T he maps are drawn from data stored in tJl e not be lI sed alone for land-use planning, planning or QMAP geographic information system (G IS), a database desig n of e ng ineerin g projects, earthquake risk developed and maintained by GNS. The QMAP database assessment or oth er work for whi c h detailed site is complementary to, and can be used in conjunction wi th , investigations are necessary. Some of th e data sets 1 Hoolihan 1977 2 Hil11974 3 Moore 1957 4 Sumosusaslro 1983 5 Chapman-Smith & Grant-Mackie 1971 6 P.R . Moore & I.G. Speden 4 unpublished maps 7 Gifford 1970 8 P.R . Moore &I.G. Speclen unpublished maps 9 Mazengarb 1988 10 Gibson 1986 11 Speden 197Gb 12 Pick 1962 & Vella 1959 13 Ongley & MacPherson 1928 14 Rail 1992 15 Kenny 1986 16 I.G. Speden unpublished maps 17 J. S. Crampton, M.J. Isaac, C . Mazengarb, & loG . Speden unpublished reports 18 Mazengarb etal. 1991a 19 Rait 1992 20 Moore 1961 21 Moore 1989a 22 Ongley & MacPherson 1928 23 J.S. Crampton & C. Mazengarb unpublished maps 24 Pick 1962 & Vella 1959 25 Miller 1926 26 Ongley & MacPherson 1928 27 Feary 1979 28 Isaac 19n 29 Moore 1961 30 Stoneley 1959, 1968 31 Mazengarb 1982 32 Hawkins 1963 N 33 Strong 1927 39 34 Strong 1927 35 I.G. $peden unpublished map 57 36 Speden 1975 & Moore 1978 37 Joass 1987 38 $avella 1992 39 Phizackerley 1962 ~O """",,!"i1ii;0= ;;ii20 kin 40 Phizackerley 1962 & leach 51 1927 50 41 Jones 1940 42 Ridd 1963 43 Weymouth 1939 44 Haw 1959c & Phizackerley 1962 Type 01 data 52 45 Bishop 1968a 0 Unpublished theses 46 Pullar 1962, Neef & Botlrill 1992 & Haw 1959c 54 55 0 """""-' pape

Figure 2 Distribution of principal data sources used in compiling the Raukumara map. Unpublished reports are held in the archives of GNS. Offshore data is from Foster & Carter (1997), Field, Uruski el al. (1997), and P. Barnes (pers. comm.).

2 incorporated with the geological data (for example, the Geological Resources Map of New Zealand data, see Chri stie 1989) have been compiled from old or unchecked The North Island axial ranges extend northeast as the information of lesser reli abili ty. Urewera Range and the Raukumara Ran ge, which termi nates in the north near th e River (Fig. REGIONAL SETTING 5) and Raukumara (YI5/616693; 1413 m) . The Raukum ara Range is almost entirely covered in native The Raukumara 1:250 000 geological map covers forest, is over 35 km wide and has a maximum elevation II 700 km' of eastern , Raukumara of 1752 m al Hikurang i. Summit heights rise Peninsula and northern Hawke's Bay. Gisborne is th e progressively from the Bay of Plenty coast toward th e largest urban area and only city; in 1996 the population axi s of the range. The topography is generaJl y steep, was 32 653. is the next largest settlement ( 1998 though flat or gentl y dipping surfaces cap man y hilltops population approximately 10600). There are a number (in cluding Arowhana, which is 1439 In high). The of small coastal sett lements (e.g. , drainage is typicall y deeply incised wilh bluffs and deep and TeAraroa) and several small settlements inland (e.g. gorges. Most rivers flow north 10 the Bay of Plenty, the , , Matawai, ). Except for major ri vers bei ng the , Otara, Motu, Haparapara, the coastal strip and the Waipaoa vall ey (Poverty Bay Kereu and Raukokore. Several major east-flowin g ri vers flats) the area is sparsely populated. The major land uses also have their headwaters in the Raukumara Range are sheep and beef farming, and exotic forestry. (Tapuaeroa, Mata, Waipaoa and Wairoa). The eastern Bay Horticulture, viticul tu re and cropping are restricted to the of Plenty coastline flanking the ran ge has small bays, alluv ial plains and terraces, main ly near Gisborne. Large with rugged headlands, wide shingled ri ver mouths and tracts of land in the north and west are covered in nati ve gravel beaches, in contrast to the extensive, sandy beaches forest, as in the Raukumara Forest Park. present near and further west. Elevated marine terraces up to I km wide and 40 m above sea level are The Raukumara Range is th e northeast extension of the present along the coast. ax ial ranges of th e North Island. To the northwest of the axial ranges (and beyond the map boundaly) lies an active Northern tip of Raukumara Peninsula volcanic arc known as the Taupo Volcanic Zone. Late Jurassic to Early Cretaceous basement rocks of the The northern tip of the peninsula is dominated by two Raukumara area and their Triassic-Jurassic equivaJents ranges Formed of erosion-resistant Matakaoa Volcanics, can be traced south along the axial ranges to Cook Strait separated by lowland valleys underlain by soft Cenozoic and beyond. Simi lar basement rocks can al so be found sedimenral)' rocks.The northern rangeextcnds ESE from on the western side of th e Taupo Volcanic Zone (for Cape Runaway to Matakaoa Point, is 3-4 km wide, and exampl e, in Coromandel and NOlthland). Mid Cretaceous up to 474 m hi gh. A discontinuous apron of elevated and you nger cover sequences similar to those of the terraces up to 60 m above sea level is preserved behind Raukumara area are present along th e of eastern the rocky coastline. Further south the Pukeamaru Ran ge North Island and in No rthland. extends inland from Haupara Point on the south side of Hi cks Bay to Oweka Stream, is up to 7 km wide and The plate boundary between the Australi an and Pacific 990 m high. Extensive marine terraces have been cut in plates propagated through the Northland and East Coast the easily eroded sedimentary rocks present between the regions in Late Oligocene to earliest Miocene time. Raukokore River mouth and Cape Runaway~ at Waihau Raukumara Peninsula is adjacent to and above the present Bay they are 3 km wide. day active pl ate boundary (subduction zone) between the obl iquely colliding Pacifi c and Australian tectoni c plates Eastern foreland (Fig. I). The seafloor expression ofthe plate boundary is the Hikurangi Trough, approximately 90 kill southeast Almost aJi the area east and south of the Raukumara of th e peninsula. The land area is part of the overrid ing Range is less than 1000 m hi gh. it contains a range of Au stral ian Plate (the fo rearc), and it is bei ng upliFted and landforms many ofwhi ch re fl ect the underl yi ng geology. deformed by the subduction process. The area is deepl y incised. All three main catchments (Waiapu, Wa ipaoa and Wairoa) extend to the flank ofthe GEOMORPHOLOGY Raukumara Range, but small e r coastal catc hments include th e Awatere, Uawa and Nuhaka ri vers. Hillside The di verse landforms onshore are described in three erosion, landsli di ng and stream aggradation are major geomorphic regions (Fig. 3; for place names see Fig. 4). problems in man y parts ofth is area. Terrace development

3 Figure 3 Computer·generated digital terrain model of the Raukumara area.The major geomorphological features labelled are the Raukumara Range including the Pukeamaru Range at the northern tip (a), the tableland in the Tauwhareparae area (b), Eastern Foreland (c) , Poverty Bay flats (d), the continental shelf (e) and continental slope (I), the Poverty sea valleys (g), and the western margin 01the Hikurangi Trough (h).

4 Oweka Stream Pukeamaru Waikura Matakaoa Point Cape Runaway / Hicks Bay Whangaparaoa River --=:!:~--\- ..r:'Y- / ______Waihau Bay -=--:-:-----=::----~ .f 1Cl-"'''''''''''''-- Karakatuwhero River Raukokore River -----~ Awatere River, Kereu River -;~~=,"",,L---- East Island Raukumara ~~,):i?!::~::.....__nkitiki, Olara River Tapuaeroa River Ruatoria Hikurangi ' ~.--- ~ MataRiver "''''iii~'--;f--'.~__Tokomaru Bay Waioeka River Tutamoe plateau

Maungahaumii ~=tl:J~!~~~ ~'tF--- Uawa River, Tolaga Bay - .y __----'~{---- Waimata >.-_-- Mokonuiorangi -tr ::;;l Range r --- )4---- Pouawa Hangaroa River ~,*>oj!~~ ,...-,rc-r'---Waimata River mouth, Gisborne

Whakapunake - ..;...."""oc1'i"'" Sponge Bay Elevation Wairoa--+---_.f:.. Moumoukai D 0 - 500m • 500 - 1000m

Wairoa River • 1000 - 1750m

Portland Island

Figure 4 Location map for places mentioned in the section on geomorphology. isex tensive in many oflhecatchments, notably the middle to Waikura and Ruatoria. Similar but smaller areas of Waipaoa River area near Whatatutu (Fig. 6). erosion are present between Waimata and Whangara, and between Pouawa and Sponge Bay. They correspond to An ex tensive erosion surface of relatively fl at- lying to areas ofstrongly fractured and faulted rocks which locally rolling topography is present in the Mata and Waipaoa include smectitic claystones . Where rocks of different headwaters at abo ut 500 m elevation (Yoshikawa el al. types are juxtaposed and mixed the topography has a 1988). A sim ilar but smaller and deeply incised surface distincti ve hummocky appearance (Fig. 7). ispresent in theWharerata area. A zoneofex Lreme erosion typified by ex tensive gully erosion, ea rthnows and East of Te Araroa and north of (including East hillside slumps ex tend s northward from the headwaters Cape and East Island) is a distinctive are" with deeply of the Waipaoa River in th e vicinily of M angatu Foresl incised drainage and tablelands ri sing up to 393 111 . SOUUl (e.g. Fig. 7), along the Mata and Tapuaeroa catchments of Te Puia gently dipping and sy ncl in al Miocene and

5 Pliocene sandstones (and minor li mestones) fo rm In coastal areas erodi ng rocky headlands are separated di stinctive, steep landforms with rem nant plateaux, as at by sandy bays. The Wa iapu. Karakatuwhero, Uawa, , Tutamoe plateau and Moumoukai. Wa iroa. and Waipaoa rivers have extensive floodplains. Prominent dip slopes are present at Whakapunake Dunes and back swamps arc locally well developed in (limestone with karst structures). Poverty Bay, in the Mahia tombolo and between Nuhaka (Iimeslone). Mokonuiorangi Range (sandslone). Gable and Wairoa (Fig. 8). Marine terraces are well preserved End Foreland (sandstone) and in the coastal cliff beside at Mahia Peninsula and Portland Island where they range the Tolaga Bay wharf (sandstone). In contrast, extensive up to 200 III elevati on (Fig. 9). ear Te Araroa marine areas underl ain by l11u dsLO ne have more subdued terraces are preserved belween 200 In and 300 III above topography. sea level.

Figure 5 View southeast toward the mouth of the Aaukokore River (Y14/390826) and the northern Raukumara Range showing the typical steep, forested hill country underlain by Torlesse rocks. The Aaukokore Thrust (outlined) separates Torlesse rocks in the hanging wall (to the right) from Tikihore Formation in the footwall . Photo CN9086114: D.L. Homer

6 Onshore physiography and geology Lewis el al. 1997). Beyond the continental slope li es Ihe Hikurangi Trough whi ch, further La the northeast, links East of Raukumara Peninsula the continental shelf is 12­ with the Kermadec Trench. The trough is 3500-4500 m 35 km wide. The shelf includes aClive fold s and faults, deep and the trough/slope boundary is taken to represent subs id ing basin s (e.g. Hawke Bay. incorporat ing th e the positi on of the plate boundary. Southeast of th e Lachlan Basi n) and fau lt-controlled structural highs (e.g. Hikurangi Trough the Pacific Plate seanoor has low relief, Ariel Bank and Lachlan Ridge, near Gi sborne) (P. Barnes except where there are seamo un ts and debris flow pers. comm.; Fosler & Carter 1997; Katz 1975). The deposits.The geology is poorly known, except for Hawke boundary with th e continental slope is at approximately Bay where there is a good network of oil industry seismi c 200 In watcr depth. The continen tal slope is irregular and surveys and a single petroleum exploration well (Hawke hUllllllocky. with structurally controll ed ridges, canyons Bay-I, 23 km south of Wa iroa and jusLoutsi de the map (e.g. Poverty Canyon) and large re-entrants (semicircular boundary). The offshore area is structurall y complex wiLh indentations along the co ntinental shelf), at least so me lhick Miocene to Quaternary sedimenLs in fault-controlled of whi ch are the headscarps of major submarine debris basins. A th ick sequence of Cretaceous and Paleogene flows (e.g. Rualoria debris avalanche; Col1ot el al. 1996; rocks is probably also present (Fi eld, Uru ski el al. 1997).

Figure 6 The meandering Waipaoa River nearTe Karaka (looking north towards Whatatutu). When this photograph was taken (1988), the lowest terrace (of Holocene age) was covered by silt deposited during Cyclone Bola. Four terraces, labelled 1, 2, 3 and 4, represent aggradational culminations of 14700, 28 000, 57000 and 90 000-110 000 years respectively. Older Quaternary lake and river deposits (Mangatuna Formation ­ c. 600 000 years) cap hill tops locally. Phato CN13129121: D.L. Homer

7 North of the peninsula the continental shelf is narrow (m inimum 5 km) and water depth in creases rapidly to 2200 m, beyond which is the extensive Raukumara Pl ain (north of map area). The continental slope is broken by the c. 50 km wide Matakaoa Re-entrant, the semicircular headscarp ofthe Matakaoa debris flow (Blackmore 1996; Carter 1998).The Raukumara Plain is underlain by some 13 km of sediment known as the Raukumara Basin (Gillies & Davey 1986; Davey et ",. 1997).

Figure 7 In the upper , the basal decollement of the East Coast Allochthon (ECA) is represented by the Waitahaia and Te Rata thrusts (middle distance).The Whakoau Fault, a low angle normal fault. separates ECA rocks from th e younger, in-place Tolaga Group (area of subdued topography in the foreground). View is to the north. Photo CNI3129/21: D.L. Homer

8 Figure 8 East of Wairoa the coastal plain is advancing seaward; former sea cliffs are visible on the inland shore of the Lagoon (left). Mahia Peninsula (far distance) is part of a rising structural high. Photo CN47895125: D.L. Homer

Figure 9 The flat surfaces of Portland Island (foreground) and Mahia Peninsula are marine terraces cut into the Late Miocene rocks. The terrace on Portland Island is 125 000 years old and about 110m above sea level. Terraces at southern Mahia Peninsula are tilled to the WNW;the tilling and uplift are related to active growth of the Lachlan Ridge, the crest of which is offshore, immediately east (right) of the peninsula. Photo: Stephen Jones, Ti'eble Court Photos, Gisborne

9 STRATIGRAPHY

The rocks of the Raukumara area are here subdi vid ed The ori ginal definition of th e Torlesse terrane was given into and described as five major units. based mainly on by Coombs el al. (1976). Later workers subdi vided lhe th eir age and their structural history: Torlesse rocks into a number oft.erranes and subterranes Lale Jurassic to Early Cretaceous basement but for some areas contl icting interpretat ions have been in -pl ace Cretaceous to Oligocene rocks given. Bradshaw el al. ( 198 1), Bradshaw (1989) and the Easl Coasl All ochthon (Earl y Cretaceous 10 Sil berling et. al. ( 1988) subdi vided the To rl esse into Oli gocene displaced rocks) subterranes, the easternmost of which (Pahau subterrane) Miocene and Pliocene rocks. and included the basement rocks of th e Rauk umara area. Quatern ary sediments. Others subdi vided the Pahau subterrane in lO two units. both of which they termed terranes - Pahau terrane. of The nature of the contact between the first two units is Late Jurassic to Earl y Cretaceous (?Barremi an) age. and di sputed in some areas. The Early C re taceo us to a youn ger (Apti an-Albian) Mata Ri ver terrane (Sporli & Oligocene rocks are subdi vided on th e basis of structural Ballance 1985, 1989). The boun dary between Pahau and hi story. In the south west oflh e map area basement rocks Mata Ri ver terran es was originally placed near th e are unconformabl y overla in by an in- pl ace Whakatane Fau lt , i.e. west of the area of the Raukumara (autochtho no us) sedime ntary seque nce of Ea rl y map (Sporli & BaJiance 1985, 1989). but laler moved Cretaceous to Oligocene age.However, in the northeast easlward by 40 km. to inlersecl the Bay of Plenty coast (nonheasl of Matawai-Te Karaka) equiva lent rocks are nearTorere. 18 kill eaSI ofOpoti ki (A ila & Sparli 1992). presenl as a seri es of thrust sheels (the East Coasl Allochthon ofMoore I988a) some ofwhi ch are di spl aced The validity of "Mata River terrane" remains unproven. at least tens of fro m their original locations If Mata Ri ver te rra ne is found to be a valid a nd , over large areas, thrust over th e equivale nt tcclOnostratigraphic unit, the name is in appropriate, since autochthonous sequence. In th e southwest a regional the Mata Ri ver catchment li es entirely within middle unconformit-y is present between th e Ea rl y Cretaceous to Cretaceous and you nger cover strata. Mortimer ( J995) O li gocene in -place seq uence and the overl ying Miocene­ subd ivided the To rl esse rocks of the eastern North Island, Pli ocene unil. The th rusl sheels o f lh e East Coast based on differences in sandstone petrographic modes. Allochthon are also overl ain by Miocene-Pliocene beds. age. bulk chemi cal composition and the kn own and inferred extent of melange belts; his work suggested there LATE J RASSIC TO EARLY C RETACEOUS may be no basis for a distinct Mata Ri ver terrane. He BASEMENT de fin ed two major basement units east of the Taupo Volcanic Zone. name ly th e Pahau subterrane and a Torlesse composite terrane previously unrecognj sed Waioeka subterrane, both of Late Jurassic to Early Cretaceous age. The boundary between Terrane nomenclature the Pahau and Wa ioeka sll bterranes was drawn at a maj or zone of melange inferred to extend south from th e Bay The indurated qumtzofeldspathic and lithi c sandstone and of Plenly coast as far as a poi nl WSW of Lake mudslone ("greywacke") of the nonhwestem Raukumara Waikaremoana (th e Whakatane me lange; Mortimer a rea have commo nl y been ma ppe d as Torlesse 1995). All basement rocks of the Raukumara area are Supergroup (e.g. Suggate et al. 1978). Torlesse rocks east of lh e Whakalane melange and within hi s Waioeka fo rm th e orth Island ax ial ranges and much of the subterrane. Two di stinct petrofacies were differentiated Soulhern Alps; they range in age from Carboniferous 10 (Waioeka petrofacies and petrofacies). This Earl y Cretaceous. subdi vision into subterranes and petrofacies was accepted by Field, Uruski et al.( 1997). The basement rocks of New Zealand are al so mapped in term s of tectonostratigraph ic terranes (e.g. Coombs el al. Begg & John slon (2000) elevated units formerly kn own 1976; Bishop et al. 1985; Bradshaw 1993; Fig. 10). The as slIbterranes (e.g.Pahau subterrane) to fu ll terrane Late Jurassic to Early Cretaceous basement rocks of lhe status. on th e basis of their presumed di screte geological Raukumara area are a part of the Torl esse composite origin s, and applied th e name "Torl esse (composite) terrane, one ofseveral Late Paleozoic to Early Cretaceous. terrane" for Torl esse rocks in general. Kamp's (1999) fa ult-bounded tectonostrati graphic units of low grade work on fi ssio n track lhe rmochro no logy of lh e metasedimentary rocks whi ch constitute th e Eastern Raukumara basement rocks found Mortimer's ( 1995) Province of ew Zealand. The monOlOnous sequences subdivision to be appropriate; he also elevated th e of indurated, interbedded sandstone and mudstone typi cal subterranes to full terrane status.Following Mortimer of the Torlesse are inferred to have accumulated mainly ( 1995), Begg & John ston (2000) and Kamp ( 1999) th e in deep marine environm ents, within an accreti onary basement rocks of the Rallkllmara area are here mapped prism. as Waioeka terrane, a part of the Torlesse composite terrane. to SEDIMENTARY AND VOLCANIC ROCKS

..~and East eo.st aIoeh1hons

w.p.p. QOl'tIPOSIIe JerT.- TOItesse ccrnpo$4e (~NorthIsa-l) Iemtne (eastem HZ) ~,... Waioe«a • ~alIMtJnds ~ -- , o ,< •

PLUTONIC ROCKS

REGIONAL TECTONIC· METAMORPHIC OVERPRINTS

eM Head Incl Whakatal'lll melanges IIIIII1 ....",,,., Gneiss

200 km

East Coast Allochthon Omaio petrofacies

Figure 10 Basement (pre·Late Cretaceous) geological map of New Zealand. Nomenclature and boundaries of North Island Torlesse and Waipapa terranes are controversial; parts of Morrinsville-Manaia and Pahau units may be correlative. Adapted from Black (1994), Mortimer (1995), Mortimer et al. (1997, 1999), Kamp (1999) and references therein; the basement terranes were in mutual juxtaposition by the late Cretaceous. The exlent of the Northland and East Coast allochthons is also shown; they were emplaced in Early Miocene time. The inset map shows present day geology of the Raukumara area.

Torlesse rocks of the Raukumara area is relati vely common (Fig. 12), wh ile melange (containing exoti c rocks) is rare. Melange includes bl ocks of chen , The major lithologies present are indurated, ahernming, spi litic basalt and limesto ne. Metamorphic minerals thinly bedded. line-grnined sandstone and l11udstone (Fig. iden tified in c lude pumpe ll yi te. pre hnite, e pidote, I I), th ick sandstone and massive mudstone, with minor laumontite, datolite, heuland ile and stilbit c; laumontitc conglomerate and pcbbly mudstone. Broken fo rm ation is by rar th e 1110st cOl11 l11o n (Feary 1974; Hill 1974;

I I Figure 11 Steeply dipping beds of - to -bedded Torlesse sandstone and mudstone beside the highway south of Omaio (Xl51168654) show the fraduring and faulting typical of these rocks. They are unconformably overlain here by Quaternary colluvial and tephric material. Photo 42148/25: D.L. Homer

12 Figure 12 Torlesse sandstone (pale grey) and mudstone at Torere Beach (X15/010505) have been disrupted to form broken formation. The cross-cutting veins (white) are almost undeformed and must, therefore, postdate the deformation which produced the broken formation. The area shown is about 1.7 m across.

Hoolihan 1977; Isaac 1977). Waioeka petrofacies Spilitic basalt, chert and red and green argill ite present at sandstones arc quartz-pool' «20%), volcanic litharcnites Te Kaha are associated with an extensive area of broken and Omaio petrofacies sandstones are quartz-rich (>20%) formation and melange (H ill 1974; Aita & Sporli 1992). fe ldsarenit es (Mortimer 1995). Similar rocks in the Motu Ri ver (e.g. X 161250450) are associated with the Big Unknown Fault. Sheared The predominant sandstone and ll1udsLOne lithofacies sandstone wi th pods of massive pyrite and chalcopyrite, ranges from centimetre- to decametre-bedded. with a maroon tu ff and cherL present at Te Kumi (Y I5/497684) hi ghl y variable ratio of sandstone to mudstone. Some were tentatively mapped as Mokoiwi Formation by in tervals are al most totall y composed of massive Pirajno ( 1979), but are now believed Lo be a part of the sa ndstone (as at the summ its of A rowhana and Torlesse. Hi.kurangi). Fine-grai ned sandstones predominate, but SQmcare medium- or coarse-graincd. Carbonaceolls plant Macroscopi c fossil s other than plant material are very material and sedimentary stru ctures are common in rare (Speden 1976a; Wilson et al. 1988). The Korangan thinner sandstone beds. Vei nin g, jointin g and fracturing stage ind icator fossil Alu.:ellina cf. radia/os/rima has been are prevalent. co ll ected fro m pebbly sandstone at Haumiaroa Point, northeast of Hawai Ri ve r, but the stratigraphic position Conglomerate is common between the Raukokore River and re lationships of the fossil iferous beds are still mouth and Waikawa Point (Fig. 13, X 141270805), where ambiguous; they may be a part ofa youn ger, chann el-fill it is present in beds up to 100 m thick. Clasts are typicall y sequence (Speden I972a, 1976a; Hoolihan 1977; M.G. well rounded pe bbles and cobbles, and there is a Lai rd and J.D. Bradshaw, pers. comm.). The Puaroan significant proportion of granitoid, silicic volcanic and (Late Jurassic) stage indicator fossil Buchia aff. plicara basic volcanic lithologies (Moore 1957). Peralkaline has been coll ected from thinly bedded sandstone and rhyalite clasts fro m Whanarua Bay have the trace element mudstone in the Matawai area (Speden I972a), but signature characteristic of, and are inferred to have been dinoflagell ate microfoss il s recovered from concretions derived from, the Early Cretaceous Houhora Complex and mudstones suggest much ofthe Waioeka terrane rocks continental-silic ic volcanic rocks of northern most of the Raukumara area are Early Cretaceous. Radiolaria Northl and (Mortimer 1995). Mi nor occurrences of in chen from Te Kaha indicate an Early Cretaceous age conglomerate have been mapped betwee n Koranga and (late Valanginian-early Barremi an; A iLa & Sporli 1992). the Waioeka Gorge (i saac 1977; Moore 1978). Beds of However, the chertlbasalt/coloured argi llite associations pebb ly mudstone with angular and roun ded clasts of typicatiy present in melange are inferred to be ocean fl oor sa ndstone and concretionary mudstone in mudstone material fau lted into th e clastic sequences as a part of matri x are well exposed along the Petipeti Road (e.g. X 17/ subduction processes. Ages deri ved from radiolaria in 100320) and at Haumiaroa Point (X 16/085553); they are chert blocks are commonly not representatiti ve of the ages interpreted as debri s fl ow deposits. of the enclosing clasti c rocks (Aita & Sporli 1992).

13 Figure 13 Conglomerate with both sedimentary and igneous clasts is common within the Torlesse rocks between Waikawa Point and the mouth of the Raukokore River. At Whanarua Bay (Y141329802) conglomerate and sandstone are interbedded. Photo CN42t40150: D.L. Homer

14 Waioeka petrofacies sandstones collected from the The contact between To rlesse and overlying rocks Waioeka Gorge - Matawai area include zircons dated by the fi ssion track method at 125 ± 2 Ma (Kamp 1999). A In the west of the Raukumara map area (i.e. west of the single Omaio petrofacies sandstone gave a zircon fi ssion Moutohora Fault), Late Jurassic to Earl y Cretaceous track age of 108 ± 6 Ma. Zircons from an Omaio Waioeka terrare Torlesse rocks are overl ai n petrofacies sandstone from Whanarua Bay are as young unconformabl y by gently to moderately dipping as c. I()() Ma (S HRIMP UlPb method; Cawood el at. conglomerate. sandstone and olistostrome breccia of 1999). The Omaio petrofacies zircons are significantl y E..1.r1y to Late Cretaceous age (the Matawai Group; Isaac younger than any yet dated from the Wai oeka petrofacies, 1977; Speden 1972 b; Speden 1975; Fig. 14). Between confirming th at the Omaio petrofacies comprises the Koranga and Matawai, basal Matawai Group beds are youngest parts of the Waioeka terrane (Mortimer 1995; locall y as old as Korangan (Aptian) but generall y of Kamp 1999). Urutawan-Motuan (A lbian) age. In the east, between Mout ohora Fault and Kokopumatara Stream, Torl esse In summary, the fossil and zircon ages indicate Waioeka rocks are succeeded by an Early and Late Cretaceous terrane rocks are of Early Cretaceous age, though perhaps sequence dominated by mudstone and -bedded locall y as old as Late Jurassic if the accepted age range sandstone and mudstone. East of Kokopumatara Stream of Buchia aff. plicaltl is correct. Torlesse and Matawai Group strata arc in fault contact.

Figure 14 West of Matawai Torlesse composite terrane sandstone and mudstone are unconformably overlain by gently dipping Koranga Formation conglomerate and sandstone; the contact is indicated by the dashed line. Matawai Quarry (centre, X17/009033) works a Koranga Formation sandstone. State Highway 2 can be seen in the centre right; the river is the upper reaches of the Motu. Photo CN42 149/3: D.L. Homer

15 In the Konmga-Matawai area the hi gh angle unconfo rmity is a sharp contact between Torlesse rocks and overlying (Fig. 15) belwccn Torlesse rocks and Matawai Group Matawai Group rocks (e.g. Laird & Bradshaw 1996). strata marks changes in the degree of deformation. induration. fossil content and lithology. These changes Though the argument is unresolved, some aspects are are interpreted to represent a significant break in accepted by most workers: deposition resulting from a period ofdeformalion, uplift no single unconfonnity surface ofEarly Cretaceous and erosion, followed by marine transgression. The nature age is proven to exist across the whole region ofthe equivalent contact east ofMourohora Fault is more angular unconformities separate Torlesse rocks contentious. Some workers favour a gradation, based on from Matawai Group covering strata over large the lack of a proven angular discordance, the perceived areas, at least to the west of the Moutohora Fau ll gradational changes in lithology and induration, overall east of Moutohora Fault, soft sediment slump si milarity oflithologies. and the gradual upward increase features and intraformational olistostrome-breccias in fossil content (as at Pakihi River, X 16/013276; Moore in Urutawan-Moluan (Albian) time represent a 1961 ; Mazengarb 1993). Olhers note the OCCurrence of period of instabilily thick olistostrome breccia and soft sediment slumpi ng at some possible Torlesse rocks at Hawai River or near the boundary, consider there is a difference in contain the same Korangan stage (Aptian) ind icator in duration, tectoni sm and fossil content, and argue th ere fossi l as the oldest Matawai Group coveri ng strata

Figure 15 On the south bank of Koranga Stream (X17/912967) vertical sandstone and mudstone of the Torlesse composite terrane are unconformably overlain by gently dipping, fossiliferous conglomerate and sandstone of the Te Wera Formation, Matawai Group.The scale is given by the figure on the far bank. Photo CN42254119: D.L. Homer

16 of the Koranga-Matawai area (Aucellina c f. indurated. well bedded conglomerate, breccia. and coarse­ radiatostriara) to fi ne-grained sandstone, with th in intercalated • zircon fi ssion track and SHRfMP UlPb ages suggest mudstones, and is locall y up to 250 m th ick (S peden 1975; some Torlesse rocks are younger than the oldest Isaac 1977). Macrofossil s are relati vely C0 l11111 0n and Matawai Group strata. indicate an Albia n (U rutawan) age (Speden 1975). The Stratigraphic and structural analys is led Mazengarb & depositional environments of the Koranga and Te Wera Harri s ( 1994) to conc lude that subducti on-d ri ven fo rmations have been interpreted as shallow marine deformation and thrust faulting cont inued through Earl y inshore shelf(Speden 1975; Isaac 1977) or alternatively, Cretaceous lime until about 85 mi ll ion years ago; thei r deep mari ne (Laird & Bradshaw 1996). Te We ra model is in part suppo n e d by the fission track sandstones are pelfographicalJy di sti nct from those ofthe thermochro nology work of Kamp ( 1999). un derl ying Waioeka petrofac ies and Koranga Form ati on, for they are texturall y and composit ionall y morc mature. IN-PLACE CRETACEOUS TO OLIGOCENE ROCKS Oponae Melange (Kmo), present locall y in th e extreme west of the mapped area, was originally mapped with in Thi s section deals onl y with the in ~ p l ace (autochthonous) the Torlesse roc ks (e.g. Feary 1979), but is now Cretaceous to O li gocene rocks whi ch underlie either the considered to be a part of the Matawai Group , since it East Coast All ochthon thrust sheets (northeast) or the apparentl y overlies To rl esse rocks unconformably, and Earl y Mi ocene un conformity (southwest), i.e. those rocks is itself conformably overlain by Karekare Formation. It which have not been displaced tectonically from where is considered to bea basal o li stostromal unit, as ori gin a Ll y they were originally deposited. proposed by Speden (l972b), and consists of angular blocks and rounded pebbles of sandstone, mudstone, coal, Early and Late Cretaceous rocks of the Matawai bedded chert , marble, basalt and oth er igneous pebbles Group enclosed in a sheared and fo lded mudstone to very fi ne­ grained sand stone mat rix. Rare macrofossil s (W16/ Raukumara Peninsula has some of the best preserved 864 188;just west of th e map boundary) and strati graphic Early and Late Cretaceous sequences in New Zeala nd constrain ts ind icate 3nAIbian (Motuan) age. Chert blocks (Well man 1959; Spedcn 1975; Crampton el al. 1995). incorporated within the melange are Early Jurassic (Feary The Matawai Group is a unit of moderately indu rated, & Pessagno 1980). in -place sedi lllentary formations of late Earl y Cretaceous to Late C re taceous age, outc roppin g a long the T hese relatively thi n late Earl y C retaceous basal southeaste rn fla nk of the Rauku mara Range. The c ong lo me rate , breccia and sand stone un its are stratigraphy varies considerably within the mapped area. conformably overlain by a thick l1ludslOne-dominated ]n the west, four un conformit y-based transgressive sequence of late Earl y CreLaceous to Late Cretaceous age sequences m'e recogni sed. Lateral facies changes suggest (Karekare Formation, KOla; Figs. 16, 17). It includes a west to east transition from shelf to bathyal sequences. intervals of th inly bedded sandstone and mudstone, and in pl aces, rare Lhi ck sandstone, tuff beds, conglomerate, The oldest 'cover' fo rmation (Koranga Formation, and illlercalations of red and green mudstone (Fig. 18). Kmk) rests with angular un conformity on Torl esse rocks Karekare Formation is characterised by re latively (Fig. 14) and is known with celtainty only over a strike abundant fo ssils, mai nly the large mussel-like inoceramid length of 25 km in the Koranga-Matawai area. It has not bivalves which are commonly present as shell beds (Fig. been recognised east of the Moutohora Fault. Il consists 17; Crampton 1996). Karekare sandstones are more of up to 150 m of indurated, fossili ferous sandstone, quartzose and less lithic than Te Wera sandstones i.e. the conglomerate, intraformational breccia and mi nor youn ger the Matawai Group sandstone the hi gher th e mudstone. Igneous clasts are mostly ofsilick tuff, breccia, textural and compositi onal maturity (Isaac 1977). rhyolite, dac ite or granitoid . wit h minor basalt and a nd esite (Isaac 1977; Mortimer 1992). Ko ra nga West ofthe Moutohora Fault Karekare Fonnation overlies Formation sandsto nes include abun dan t fresh and partly inLerfingers with Te We ra Formation, and volcaniclastic material and they are petrographi ca ll y ranges in age from Albian Lo Turonian (Urutawal1 ­ indistinguishable from sandstones of the underlyi ng Mangaotanean). The Karekare FormaLio n in this area is Wa ioeka petrofacies of the Torlesse composite terrane up to 1220 m thick (Speden 1975); it consists main ly or (I saac 1977). mudstone, with intercalations of thi nly bedded sandstone and mudstone, and rarely, sandstones up to several Te Wera Formation (Kmt) is present over a simi lar area, th ick.ALKoranga a prominent strike ridge is fo rm ed by unconformabl y overl ying both Waioeka terrane (Fi g. 15) the Choveaux Sandstone Member, a 16 m thick interval and Koranga Formation. It co mprises moderately of sandstones with lenses of granul e conglomerate and

17 breccia (Speden 1975).The Raukumara Series Karekare rocks here are too thin ( 100m at Koranga Bridge) to differentiate 011 a 1:250000 map.

East of Moulohora Fault, Karekare Formation direct ly overl ies Torl esse rocks (Wai oeka terran e) and ran ges in age from Albian to Santonian (Urutawal1 -Pi ripauan).The basal or near-basal Karekare Formation commonly consists of mudstone wi th slump folding and otber soft sediment deformation (Pakihi Ri ver, X 1610 13276) and sedi mentary breccia (up to 250 m thi ck in Kokopumatara Stream, Y16/345329). Six stages of the ew Zealand geologicaltimc scale arc defin ed from the biostratigraphy of Karekare Formation strata exposed in the Mo Lu River near Motu Fa ll s (Clarence Scries ~ Urutawan, Motuan, Ngaterian), and Mangaotane Stream (Raukumara Series; Arowhanan, Mangaotanean, Teratan) (Well man 1959). In the reference section at Te Stream, near Motu, the Karekare Formation is 2650 m thick (base not exposed and top eroded), mainly mudstone, but including 5 discrete intercaJati ons of thinly bedded sandstone and mudstone which range in thickness from 60 to 190 m (Isaac 1977). The thinly bedded units are useful markers in that Lh ey can be traced southwest and nOl1heast for aL least 10- 15 km. East of Kirk's Clearing (X 16/210240) the otherwise monotonous blue-grey mudstone typi cal of the Karekare Formation incl udes several bedding­ parallel intervals of red mudstone and minor green Figure 16 Vertically bedded sandstones (pale) and mudstones mudstone, commonly 5- 10 m thick (Fig. 18). The red (blue-grey) of Earty Cretaceous Karekare Formation in the banks and green mudslO nes and blue-grey mudstone of the Motu River (X161185279) . Photo: J.S. Crampton immediately overl yin g them are typically devoid of fossi ls, i. e. they represent barren zones in an otherwise fossiliferous sequence. The barren zones define the range zo nes of individual inoceramid species; below the coloured mudstone shown in Figure 18 the key foss il is

Figure 17 In places Karekare Formation blue-grey mudstones contain shellbeds - in this case of the giant mussel-like bivalve Magadiceramus? rangatira rangatira, the index fossil of the Arowhanan stage (Mangaotane Stream, X1612793 12). Photo: J. S. Crampton

18 Figure 18 A prominent red mudstone bed within Late Cretaceous Karekare Formation at Mangaotane Stream (X 161 291300). Above the red mudstone the more typical blue·

-~- - '-'::': grey mudstone contains ... r'_ ...... -__~.. _ --. .;. , ~ ",:-: .. inoceramid fossils indicative of the Mangaotanean Stage; below it the fossils are Arowhanan. Photo: J.S. Crampton the very large Magadiceramlls? rO f/ gafira rallgafira, but as thi ck as 14 m. In places beddin g is disrupted by above it the key foss il is Cremnoceramus bicorrLIgattis intervals of intrafonnational slum ping up to 20 m thick. fl/afwllutlS (Crampton 1996). The origi n of th e red The form ation has a known max im um thi ckness of mudstones and their influence on the fossil s are poorly 1400 m and the known age range isAl bian to Cenomanian understood. (Motuan-Ngalerian). Waitahaia sandstones are apparently less feldspath ic than Karekare sandstones (Kenn y I984a; In Kokopumatara Stream the lower part of the Karekare her Hi kurangi Beds), perhaps because they were deri ved Form ation incl udes mudstone, breccia and sandstone mainly from Omaio petrofacies rocks. lithologies showing evidence ofso ft sediment slumping; the lowerm ost 90 m may be a sin gle slump breccia. Moanui Formation (Kmm) has a very restri cted Breccia clasts are intraformatio na l and incl ude blocks of distribution; it covers a small area between the Koranga fine-grained sandstone up to 10m thick, calcareous and Kotepato fau lts whi ch is mainl y west of the concretions and clasts ofgranule conglomerate to coarse­ Raukumara map area. It consists of fossiliferous, grained sandstone, enclosed in a mudstone matri x. moderately indurated mudstone to very fine-grained Inoceramid prisms are common. Promi nent intercalati ons sandstone with lenses and beds ofconglomerate, breccia, of thinly bedded sandstone and mudstone present hi gher pebbly sandstone and pebbly siltstone (Moore 1978). It in the sequence in clu de th in lenses of fossiliferous is up to 500 m thi ck an d the known age range is conglomerate, rip-up clasts and abundant plant materi al. Cenomanian to Coniacian (Arowhanan-Teratan). Moanui They match the Wai tahaia Fo rmation as mapped further Fonnatio n is a lateral correlati ve of Karekare Formation, east (see below), suggestin g that locall y th e two deposited as a transgressive seq uence in an inner shelf fo rmations interfinger. Near Arowhana and to th e east, enviro nment. Karekare Formation of Late Cretaceous age unconformably overli es and on laps Waitahaia Fonnation; Early and Late Cretaceous rocks of Ihe Rualoria the overlyi ng Karekare Formation ranges in age from Group Cenomanian to Coni acia n (Ngateri an-Teratan). In the easternmost outcrops (e.g. Puketoro Stream,Y 15/ An area of Late Cretaceous, centimeLre- to metre-bedded, 55 14 10), the Karekare Formation consists of thinl y fine-grain ed sandstone and mudstone at lower Mata bedded sand stone and mudstone passin g gradationall y Ri ver, prev iously mapped as Tikihore and Tapuwaeroa up ward into bedded mudstone. fo rmations of the East Coast All ochthon (Moore et al. 1989), is now thought to li e stru cturally below th e basal East ofArowhana, Karekare Formation is unconform ably thrust, i.e. the beds are apparentl y in-place (Rait 1992). underlain by centimetre- to deci metre-th ick, well bedded This requires some revisionof strati graph ic nomenclature, alternating sandstone and mud stone, with mino r since: conglomerate, pebbly mudstone and tuff (Waitahaia Black's ( 1980) defi nition ofTikihore Formation was Formation, Kmh). Rarely, individual sandstone beds are for slructuraUy complex areas now recognised to

19 be within the East Coast Allochthon (Mazengarb decimetre- to metre-bedded, sandstone-dominated, el al. 1991a; Field, Uruski el al. 1997) alternating sandstone and mudstone beds present locally he suggested no group name at Mahia Peninsula (e.g. Webb 1979) are also inferred to no type section was nominated, but the reference be au tochthonous Tikihore and Tapuwaeroa formations, sections are both within the East Coast All ochthon for they lie well south of the inferred southern limit of • MazengarlJ el al. (l99 Ia) included Tikihore and the East Coast Allochthon. In south ern Hawke's Bay and Tapuwaeroa formations in their RU3toria Group Wairarapa si milar beds have been mapped as Glenburn according to their definition, "Ruatori a Group Formati on (Field , Uruski et al. 1997). enco mp asses al l primari ly sed imentary all oc hthonous formations underl y in g th e Late C retaceous to Paleocene rocks all ochthonous part of the Tinui Group..." the intent was thal Ru atoria Group was to apply Fro m the western map boundary ncar Koranga as far 10 the allochthonous units, but not to the northeasl as Ihungia the Matawai Group is overlain by autochthonous units. the mudstone-dominated Tinui Group (Moore et al. Ruatoria Group is therefore expanded to include 1986) of latest Cretaceous to Paleocene (Piripauan­ allochthonous Tikihore and Tapuwaeroa rocks, and also Teurian) age. As the Matawai Group rocks were fo lded, the apparently autochthonous equivalents_ It is lherefore uplifted and, in some areas, deeply eroded before analogous to Tinui Group which has components (e.g. deposition of the Tinui Group, the contact between the Whangai Formation) in both the autochthon and the East two is a low to mooerate angle unconfomlity of regional Coast Allochthon. extent.

There is near-continuousexposure of 1060 m ofTikihore Over a distance of about 100 km. from Te Hoe Ri ver in Formation (Kri) and Tapuwaeroa Form,ltion (Krp) the southwest (50 km beyond the Raukumara map in the lower Mata Ri ver area (Y 15/648473), in a boundary) to Moutohora inl-he northeast, the basa l T inui structurally si mple settin g. Inoceramid foss ils indicate Group beds are massive to we ll bedded, relatively the sequence has an age range of Cenomanian to quartzose fine-grained sandstones, with minor glauconitic Sa nton ian (Arowhanan-Piripauan). siltstone and glauco nitised siltstone breccia (Tahora Formation, Kit). Tahora Formati on is inferred to have The Tikihore Formati on is mainly centi metre- to metre­ been deposited in beach to mid shelf environments bedded, alternating, fine-grained sandstone and following renewed marine transgression in Piripauan time mudstone. Sandstones typically show normal grading, (Crampton & Moore 1990; Isaac et al. 1991 ). Within the with common sole structures, trace fossi lsand incomplete area covered by the Raukumara map the Tahora Bouma sequences; deposition is inferred to have been Formation is typically less than 50 m thick and present from turbidity currents. Five sedimentary cycles are over areas too small to differentiate at 1:250 ()()() scale. recognised, each starting with a thick (up to 20 m) slump horizon which is overlain by thick (up to 3 m) len ti cu lar Further east, up to 100m of upward-fining, we ll bedded sandstones, fo ll owed by the more typical alt ernating sa nd stone and mudstone (Owhena Formation, Kio) is sandstone and mudstone (Laird el al. 1998a, 1998b). present in th e sa me stratigraphic position over a Bi oturbated hori zons and intervals are common within geographi ca ll y rest ri cted area along Waitahaia Ri ve r mudstone and there are zones of abundant inoceramid (Phill ips 1985). The immediately underlying Karekare fossils, so me up to I m across, and ap parently litlle Form at ion is intense ly burrowed, w ith abundant tran sported from growth position. It has been argued that ca lcareousconcreti ons. Owhen3 Formation is interpreted inoceramids in growth position indicate Tikihore as a deeper water equivalent of Tahora Formation, Formation accumu lated at relatively shallow depths, but deposited by sed iment grav ity flow mechanisms in outer the use of life position alone as an indicator of shelf and slope environments. paleobathymelry is now known 10 be unreliable (Crampton 1996). The extent of the formation, its great Tinui Group basal sandstone facies are confonnably and thickness. monotonous facies and sedimentary structures in places gradati onally overlain by the Whangai suggestT1kihore Formation accumulated as a submari ne Formation ( Kiw), a thick, mudstone-dominated unit fan or fans. in deep marine (slope to bathyal) widely recognised throughout eastern New Zealand environments (Mazengarb 1993). (Northl and , Raukum ara Peninsula, Hawke's Bay­ Wairarapa and Marlborough) and in adjacent areas At Mata River the Tikihore Formati on passes upward offshore (Lillie 1953; Moore 1988b; Field, Uru ski el al. gradational ly into the sandstone-dominated Tapuwaeroa 1997). The Whangai Form ati on typicall y consists of300­ Formation ; th e co ntact is pl aced at a Coni acian (Teratan) 500 m of nonca lcareous and ca lcareous shale and intraformational breccia unit 22 m thi ck. Late C retaceo us mudston e. In western areas the formation is typi ca ll y

20 siliceous and massive (Western Facies of Moore 1988b), Eocene and Oli gocene rocks and in eastern areas (including with in the East Coast All ochthon) it is more calcareous and better bedded Deposition of mud-rich sediments continu ed throughout (Eastern Facies). Eocene and O ligocene time over much of what is now the East Coast region, including th e area of th e Several lithol ogicaJ ly distinctive members of regional Raukumara map (the Mangatu Group; Mooreel al. 1986). extent have been mapped (Moore J988b) but only one Ln the southwest of the Raukumara map area th e Waipawa can be differentiated on the map. Kirks Breccia (Kik) is Formati on is co nform abl y overl ain by Wanstead known only from Kirk's C learing in the middle reaches Formation (Egw), whi ch consists of up to 200 m of of the Motu River. It consists or up to 200 m ofchann el­ poorly bedded, bioturbated, green-grey to blue-grey, fi ll ing, mau'ix- to clast-s upported breccia-conglom erate caJcareous, glauconitic mudstone, with minor alternating of angul ar to subrounded, fi ne-grained sandstone and glauconitic sandstone and mudstone, and loca lly, mass ive mudstone clasts derived from the underl ying Karekare muddy greensand . Mudstones contain a high proportion Formation. Many clastscontain Late Cretaceous (Motuan of smectitic cl ays and are commonly, th ough wrongly, or A rowhanan ) macrofoss il s, bu t microfoss ils fro m the referred to as bentonites. Wan stead clays accumulated breccia matri x indicate a late Piripauan to ea rl y fro m background sedi mentati on in a deep ocean bas in , Haumurian age. The unit is interpreted as a submari ne while true benton ite clays are derived from alterati on of debris fl ow depos it, generated by slumpi ng associated volcani c tephra or tuff (see Fergusson 1985). Landforms with a growing fold (Moore 1989a). The Raka uroa developed on these lithologies are typi call y unstable Member (200-300 m th ick) is regio nall y extensive and becau se of the cl ays and outcrops are often marked by consists of hard, genera ll y poorl y bedded, weak ly fi ssile, slumps and earthflows. South west of M atawai the noncalcareou s mudstone, dark to mediu m grey in colour overl ying Weber Formation (Ogw) rests unco nform abl y when fresh, bu t weatheri ng to white or very pale grey, on Wanstead Formation, but may overlie it co nformab ly often w ith a rusty appearance. M in or assoc iated in th e east, as in the area of Waerell gaokuri (P.R . M oore lithologies include th in beds of glauconitic sandstone, & H.E.G. Morgans pers. comm.). It consists ofup to 400 calcareous concretions, chert and ca lcareous beds. The m of calcareous, al ternatin g, glauconitic sa ndsto ne and co mmonly overl ying Upper Calcareous Member consists mudstone, and li ght grey bioturbated, calcm'eous massive of up to 200 m of poorl y bedded, medi um grey to light mudslO ne. The W anstead Formation and Weber blue-grey weathering, slightly to moderately calcareous, formationsare ofPaleocene to Oligocene age (Joass 1987; micaceou s, siliceou s mudston e with rare calcareou s Field , Uru ski el at. 1997); foramin ifera suggest depositi on concretions, pyrite nodules, glauconitic sandstone and was mainl y at mid bath yal depths. brecc ia beds. ln the Waitahaia River area, cenlimetre- to deci metre-bedded sandstone, siliceous mu dstone with THE EAST COAST ALLOCHTHON chert nodu les and moderately ca lcareoll s mudstone are mapped as a part of the Porangahau Member (Moore Large scale displacements of Cretaceous and Cenozoic 1988b). The Whangai Formation is in fe rred to have rocks were fi rst recogni sed in Raukumara Peni nsul a by accumulated in a regionally extensive ocean basin, mainly Stoneley ( 1968) who identified and mapped a series of at bathyal depths (Wil son & Morgans 1989; Lecki eel al. 15 gentl y to moderately dipping thrust structures in the 1995). M a un gaha um i area, east o f Matawai (Fig. 19). Sub sequent mapp ing else wh ere ha s confirmed th at Whangai Formation is co nformably and gradationall y between Matawai and East Cape large areas ofCretaceous overlain by the Waipawa Formation (or Waipawa bl ack to Ol igocene rocks are all ochthonous, di splaced at least shale), a distincti ve unit of very poorly bedded, dark tens of kilometres, and poss ibly hu ndreds of kilometres, brown-grey to brown-black, moderately soft to hard, fro m th eir ori ginal sites of deposition (the Eas t Coast noncalcareous micaceous mudstone of Late Paleocene All ochthon; Moore 1988a; Rait 1992; Fi eld, Uru ski el (mid to late Teuri an) age (Moore J988b; Moore 1989b; al. 1997; Rait 2000a). Diffe re ntia ti o n of the Leckie el al. 1992). Typical samples of the shale have 2­ autochth onous and allochthonous roc ks is based mainly 6% TOC (total organ ic carbon) and th e un it has by far on differences in stru ctural style. For example, strata the hi ghest hydrocarbon-generati ng potential of any East overl yin g the Te Rata-Waitahaia Thrust are strongly Coast source rock (Field, Uru ski el al. 1997). Waipawa deformed by north west-trend ing fo lds and low angle Formati on is locall y absent and generall y less than 20 m thrusts, whereas those below are only gentl y deformed. thick.Foraminifera indicate deposition was at outer shelf A ll pre-M iocene un its north of Te Pu ia are stro ngly to upper bathyal depths (Field, Uru ski el al. 1997); deformed. Age reversals (i.e. old rocks now overl ying paleogeographic and geoche mi ca l studi es suggest younger rocks) are also present with in the allochthon. depos ition was restri cted to environm ents near the top of The Matakaoa Volcanics, be li eved to be amongst th e the conti nental sJope (Kill ops el al. 1996). oldest rocks of the all ochthon, and emplaced in the most

2 1 di stal. oceani c settin g. are now at the top and back of D iscrete. lithology-based uni ts have been differentiated the overthrust sequence (Rait 1992; Field, Uruski el al. and mapped wi thin the all ochthon (e.g. Mazengarb el al. 1997; Rait 2000a). Over large areas the all ochthonous 199 1a). Many but not all have lateral correlati ves wi thin rocks have been thrust over the top of th e in-pl ace th e in -place (autochthonous) sequence to the south west. Cretaceous to earliest M iocene seq uence. T he all ochthonous un itscommonl y represent deposition at greater depths th an equi valent s within the in-place The thrust sheets id entified by Stoneley are beli eved to sequence (Fi eld , Uruski el al. 1997). be th e south wes tern marg in of the alloc hthon and equivalent in-pl ace beds are present in the immedimely Alm ost al l the rocks of the East Coast All ochth on are of adj acent area, ncar Matawai . T he so utheas t limit of the late Early C retaceous to Oli gocene age. D etailed all ochthon is obscured by the overlying Mi ocene­ mapping, facies anal ysis, paleo ntology and structu ra l Pliocene seq uence: it probably ex tends east from Te interpretati on indicate th at th e thrust sheets were Karaka to meet th e coast in th e area of Whangara. emplaced mainl y towards the SSW, in Early Miocene 20 km northeast ofGisborne (Field, Uruski el al. 1997). time. The range oflithologies, ages ofthe displaced strata.

Figure 19 Southwestward-di rected emplacement of the East Coast Allochthon formed an imbricate stack of thrust slices near Matawai (the hill in the foregrou nd is at X17/115095;see Stoneley 1968). The approximate position of thrust faults and folds are shown .The dotted line marks the base of the Miocene sequence which overlies Wanstead Formation unconformably.The hig h, bush-covered scarp in the left distance is Maungahaumi . The view is towards the southeast. Photo CN42078110: D.L. Homer

22 structural style, direction of emplacement and timi ng of for II km. Pirajno termed them a "s pilite-keratophyre" emplacement ofthe East CoastAllochthon are all similar associat ion; analyses suggest the basa lts are subalkaline, or ide ntical to those of the Northland Allochthon of either mid ocean ri dge or back-arc affinity, and simi lar (Ball ance & Sporli 1979; Brook ef al. 1988; Isaac ef al. lO the MatakaoaVo lcanics (M ortimer 1992; Sewell 1992). 1994; Isaac 1996). Early a nd Late Cretaceous sedimentary rocks Early Cretaceous to Eocene igneous rocks T he allochthonou s equivalent of the in-place Matawai Earl y Cretaceous to Eocen e submari ne ba saltic lava, Group consists mainly ofcenti metre- to decimetre-bedded pillow lava, brecciated pi llow lava, hyaloclastite breccia al ternming sandstones and mud stones (the R uatoria and tu ff (Mala kaoa Volca nics, Kov, Kog, ) form G roup; Mazengarb ef al. 199 1a) with intervals of thicker two low ranges at the northern tip of the Raukumara sa ndstone and mudstone, minor conglomerate, and Peninsul a, namely the Matakaoa massif between Cape sedimentary brecc ia. Several lithologic units are Run away and M arakaoa Po int, and the Pukeamaru mass if di ffere ntiated. T he late st Cretaceous and Paleocene whi ch ex tends inland southeast of Hi cks Bay. A small sedimentary rocks of the alJ oc hth on are included in th e outlier ofsim il ar volcani cs is prese nt atTe Kiwikiwi Hill , T inui G roup. 9 km south of Te Araroa (Moore & Challi s 1985). The volcani c rocks are mainly subalkaline and tholeiitic in A ltern at in g ce nti metre- to dec imetre-bedded, fine- to co mposition. tn pl aces the eruptive rocks have minor medium-grained mid grey sa ndston e and dark blue to intercalati ons of sa ndstone, mudstone, limestone and black mudstone present over a large area in theTapuaeroa chert , and they are intruded by dikes and sills of basall, vall ey are mapped as Mokoi wi Formation ( Krm ; dolerite and gabbro. Speden 1976b; Gibson 1986; Fig. 20). Small er areas of M okoiwi Formation are present further sou th (M azengarb Deta iled stud ies have bee n carri ed out in coastal areas ef a t. 199Ia). Inocera mid fo ss ils are common and in where Matakaoa Vol canics are typically well ex posed in places mudstone bedsconta in calcareollsco ncretions. The low cli ffs and shore platforms (Gifford 1970; Pi rajno formation is typica lly highly tectoni sed and is in many 1980; Rutherford 1980). K-Ar dating of lavas from lh e pl aces broken formation. It includes lenso id al sa ndstone relatively fres h coastal ex posures gave Late Eocene to masses mapped as Taitai Sandstone Mem ber (fron t Early O li gocene ages (Brothers & Delaloye 1982), but cover). Taitai sand stone is mass ive, poorl y sorted, dark th ese are inco mpatibl e w ith th e Earl y C retaceou s grey to grey-gree n and fin e- Lo coarse-grained. L ocall y it (Albi an), Late Cretaceous, and Late Paleocene to Earl y co ntainsconglomerate and brecc ia bands up to 15 m thick. Eocene ages determined fro m fo ss ils contained in the It forms the moun tains of W harekia and Aorangi, and intercalated sedimentary rocks (Strong 1976, 1980; Sporli several other smaller mass ifs in the vicini ty. At M oun t & Aita 1994). It is inferred the lavas are lOo altered fo r Taitai itself (Y 15/685553), ty pi cal well bedded Mokoiwi accurate dating by the K-A r techn iqu e. sand stone and mudstone is un confomably overl ain by an up ward-fining breccia- and sandstone-dominated uni t Sporli & Aita (1 994) suggested the Matakaoa Vo lcanics considered by Speden ( 1976b) to be suffi ciently different are possibl y up to 10 km th ick. However, it is not yet fro m Tai tai Sandstone to warrant separate formation status po ss ible to determi ne either th e present thi ckn ess or the (Ma ngao hewa Fo rmation).A lte rnati ve ly, the ori ginal stratigraphic thi ckness because of the structu ral un conformi ty may represe nt th e sc oured ba se of a complexity, the likelihood of im bricati on and lack of submarine channel-fill sequence, as seen in som e Taitai marke r horizons. Se we ll ( 1992) infe rred th e y Sa ndstone masses; the unit is here incl uded in Taitai accumulated in a marginal basin adjacent to an island Sandstone. Igneous clasts in the conglomerates incl ude arc but Mortimer & Parkinson ( 1996) suggested they granophyre, rhyolite. rhyodaci te, dacite, tuffand vesicular could be an onshore fragment of the large Hikurangi basalt (Mortimer 1992, 1995; Speden I976b). Small areas Plateau igneous provin ce. Matakaoa Vo lcani cs are of conglomerate in the Waitahaia- Pu ketoro area (e.g. correlati ves of the Tangihua Complex rocks present Y 16/540395) are includ ed in the Taitai Sandstone even within the Northland All ochthon (I saac ef al. 1994). though they lack significant sandstone.

In the northern Tapuaeroa vall ey the Earl y Cretaceous M okoiwi Form ati on is fau lted againstTorlessecompos ite M okoiwi Form ation (see below) incl udes a somewhat terrane basement in the head waters of the Raukokore di scontinuousstratiform band ofmafi c lavas, intermediate Ri ver and , elsewhere, is thru st over in-place Matawai and and silicic tuffs, and tuffaceo us sediment s informall y T inui gro up strata. A ll known basal contacts are fau lled. known as the Rip Volcanics (Krr;Piraj no 1979). The T he stratigraphi c relations with youn ger un its are al so band is up to 600 m th ick and can be fo ll owed laterally un certai n. 1n the headwaters of the Mangaoporo Ri ver

23 Figure 20 Folded centimetre- to decimetre-bedded sandstones and mudstones typical of the Mokoiwi Formation exposed in the eastern bank of Mangawhairiki Stream, Tapuaeroa va lley (Yl 51617591 ). Photo CN42277/5: D.L Homer

an indurated and deformed mudstone-dominated unit of Fossiliferous, centimetre- to metre-bedded, alternating Albian (Motuan) age, considered to be Mokoiwi fin e-grain ed sandstone and mud stone, typi cal ly less Form ati on, apparently grades conformably in to less indurated and less deformed than Mokoiwi Formatio n, indurated rocks mapped as Tikihore Formati on (see is present over a large area north of the Tapuaeroa Ri ver below). The thickness of the Mokoiwi Formati on is to th e crest of th e Raukumara Range and the difficult to estimate because of the unresolved structural Kopuapounamu River, and over a large area in the complexit y. Speden ( 1976b) estimated a thickness of headwaters of the Waipaoa and Mata rivers, Mangatu 900- 1200 m. Forest (Tikihore Formation, Kri; Black 1980; Rait 1992; Mazengarb 1993). Small areas of Tikihore Macrofossil s and dinofl agellates suggest an age range of Fonnation are present elsewhere, for example at Orete Albian to Cenomani an (Motuan-Ngateri an; Speden Point and the mouth of the Raukokore River. Alternating I976b; Wilson 1976). Mokoiwi Formation sand stones sandstone and mudstone make up by far the greater part and mudstones are inferred to have been deposited in a of the unit (Fi g. 2 1), but locall y either sandstone (as in moderately deep water turbidite fa n complex. Taitai Mangaoporo Ri ver catchm ent ) or mudstone may be sandstones represent channel- or can yon-fill deposits dominant. A mudstone-dominated variant ofTeratan age within the fan system. The Rip Volcanics were fonned covers a large area north of the Tapuaeroa valley and is by sea fl oor volcanism within the oceanic plflte on which differentiated on the map. Minor lithologies include red, Mokoiwi Form ati on was deposited. g reen and purpl e mudstones, slump horizons, conglomerate, breccia and rare flow basalt (Mazengarb ef al. 199Ia).

24 Figure 21 The shore platform at Raukokore (Y14/413844; facing west) exposes steeply dipping, Late Cretaceous Tikihore Formation alternating sandstone and mudstone; the direction of younging is to the left. TheTikihore Formation in this area is about 3000 m thick. Photo CNI2973136: D.L. Homer

sandstones are typically graded with Bouma sequence Within the East Coast All ochthon the formation is sedimentary structures. Piripauan in oceramid s (e.g. typicall y thinner bedded and more monotonous than in /. australis ~Uld /. pacificLis pacificus, Crampton 1996) the lower Mata River. lnoceram id fo ssil s are common in are comm on in coarse-grained sand stone and pebbly places, but conspi cuous barren zones are present in the sandstone beds, as is the sma ll oyster OSfrea lapillicola, coastal secti ons north of the Raukokore Ri ver. At Grete a characteristic Fossil. Tapuwaeroa Fo rmation is 1150 m Point th e Teratan interva l includes 130 m of alternatin g thick at Wa io ro ngomai River, the type secti on centimetre-bedded green mudstone (siltstone), red and (Mazengarb 1993), and it ranges in age from Coniacian green muddy sandstone, and g rey cross-bedded to Campani an (latest Teratan-Hau muri an). sand stone, perhaps of sim ilar origin to the coloured mudstones present within th e correlati ve Karekare Late Cretaceous to Paleocene sedimentary rocks Formatio n at Mangaotane. Whangai Formation (Kiw) rocks within the East Coast Tikihore Formation is estimated to be up to 3000 m thi ck. Allochthon are mai nl y attributed to the Eastern Facies The base is commonly a fau lt contact. North oFTap uaeroa (Fig. 22; Moore 1988b). The rocks consist of poorly River the Tikihore Form ation grades up ward into the bedded, light blue-grey weathering, medium grey, slightl y overl yin g Tapuwaeroa Formation and the two may be, in to moderately calcareous, micaceous, siliceous mudstone part, lateral eq ui valents. Wh ere there is no Tapuwaeroa of th e Upper Calcareous Member and well bedded, li ght Formati on the Tikihore Formation grades upward into grey to white, hard, moderately calcareous mudstone, in Whangai Form ation. The kn ow n age range is places with beds of g lauconit ic sand stone, of the Cenomanian to Santonian (Ngaterian-Piripauan). Porangahau Member. The form atio n rests conformably on th e Tikih ore and Tapuwaeroa formations wi th a The Tapuwaeroa Formation (Krp; Wellman 1959; gradatio nal contact. The largest s in g le area of Mazengarb 1993) consists of moderately indurated, all ochthonous Whangai Formation covers about 75 km2 decimetre- to metre-bedded, sandston e-dominated, in the headwaters of the Waipaoa River, thrust over alternatin g sandstone and mudstone, with min or younger rocks of the Weber and Wanst.ead formations, conglomerate, breccia and mudstone. Large areas of and overlai n by Tolaga Group mudstonc of Early Miocene Tap uwaeroa Fo rmation are present within the East Coast age. Large areas of Whangai Formation are present in All ochthon between th e Tapuaeroa and Waikura va ll eys, the vici nity ofthe confluence of the Mata and Tapuaeroa northern Raukumara Pe nin sula. ri vers, near Ruatori a. Here, Whangai mudst.one is thrust over Tapu waeroa Formation, overthrust by a structurall y Tapuwaeroa sandstones are more quartzose than those hig her thrust sheet of Early Cretaceous Mokoiwi of older Ruatoria Group Formmi ons and contai n more Formation and un confor mabl y overlain by in-place plant frag ments and carbonaceous material, glauconite Miocene-Pliocene sand stone of the Mangaheia Group. and mi ca. Ind ividual sand stones are up to 6 m thi ck; Porangahau Member calcareous mudstones are present

25 Figure 22 Chevron folds in well bedded Whangai Formation mudstones on the bank of Waimatau Stream (Y l 61382235). The direction of younging is to the right and the folds are overturned. This style and intensity of folding, invotving shallow dipping axial planes, is common within the East Coast Allochthon. at Wairamaia Stream (near East Cape) and at Mahia di sti nctive facies. common in areas of melange within (Moore I988b). The Upper Calcareous Member is about the East Coast Al lochthon and in some structura lly 500111 Lhi ck in the reference secti on at Te Weraroa Stream complex areas of melange and d iapirs beyond th e (Y I6/3 17 197); the total stratigrap hi c thi ckness of the allochth on fro nt. Wa nstead Form ation is apparently lip Wh angai has been estimated to be as great as 900 m to 300 111 thick. The known age ra nge is Late Paleocene (Moore 1988b) but th ere may be un detected structural to Eocene (Te urian-Run angan), as for Wa nstead repetition. Formation within the in-place sequence.

Whangai Fonnation wit hin the allochthon is conformably The conformabl y overl ying Weber Forma tion (Ogw) overl ain by up to 50 m of very poorly bedded, grey to consists of up to 900 m of poorly bedded, pale grey brown-black, moderately soft to hard , noncalcareous calcareous mudstone with thin , glauconitic sandstone mudstone of the Waipawa Formation (Piw). Only one beds and muddy limestone. In the Mangatu area limestone area is large enough to show on the 1:250 000 map: in is up to 500 m thick. Foraminifera indicate the Weber the upperWaipaoa va ll ey Wh angai Formati on includes a Form ati on is mainly of Oli gocene (Whai ngaroan­ thrust sli ver of Waipawa mudstone which can be traced Waitaki an) age. laterali y for c. 5 km (Mazengarb e1" I. 199 1a). MIOCENE AND PLIOCENE ROC KS Eocene and Oligocene sedimentary rocks Both the Earl y Cretaceous 10 O li gocene in -place sequence Eocene to Oligocene rocks present with in the East Coast and the East Coast All ochthon are unconform ably All ochthon are similar to equivalent rocks in the in -pl ace overl ain by a structurall y simple sedimentary sequence sequence and are incl uded in the same lithostrati graphic of Earl y Mi ocene to Pliocene age (S toneley 1968: Moore unit (Mangatu Group). Wanstead Forma tion (Egw) el/ll. 1989: Mazengarb e1 /II. 1991 a). The unconfo rmity conformably overlies Waipawa Formation and consists marks a pronounced change in the e nvironment of predominantly of pale grey-green calcareous mudstone. deposition. The underlyi ng Mangatu Group is mainly in places with intercalated beds ofmid to dark green (red­ clay-rich pelagic mudstone and limestone. whereas the brown when deeply weathered). glauconitic and lithic overlying Earl y Mi ocene rocks are terrigenous and much sandstones. A few sandstones are up to 20 m thick and th icker, cont ai ning sequences of massive blue-grey some are well cemented by calcium carbonate. At Port mudstone. alt ernatin g centimetre- to metre-bedded Awanui (Z 15/89760 I) the format ion shows sandstone and mudstone. and massive sandstone, with intraformational slu mp fo lding. and conglomerate and lesser conglomerate and tuff. Emplacement of the East pebbly mudstone contain clasts of Waipawa Formati on Coast All ochthon. a nd th e subseque nt c ha nges in up to 3 m across. Coloured (red-brow ll , white, green­ sedimentatio n and deform ation style, are consequences grey) calcareous and noncalcareous. smectiti c clays tone of a major tectonic event associated with the onset of with th in, fi ne-grai ned, glauconiti c sandstone beds is a subducti on at an acti ve plate boundary between North land

26 and Marlborough (Ballance 1976; Pettinga 1982; Rait el 1000 m thiCK; there isconsi derable local variation in both al. 199 1). Detailed stratigraphi c subdi visio ns ha ve been thi ckness and fac ies. established for some local areas (e.g. Kenny 1980; Joass 1987; Savell a 1992). However, lateral changes in facies Igneous pebbl e conglomerate (MIc; the thungia igneoos and thi ckness make it difficult to correlate indi vidual uni ts co nglomerate of M cKay 1887) is co mmon at or near th e between such areas. The lithostrati gra phy adopted here base of theTo laga Group from Oweka Stream in the nDlth is based on that of Mazengarb el al. ( 199 1a) who, in the (Y I4/647875), Tarnd ale in the west (Y I613 111 21) and Yl6 area, subdi vided the Miocene-Pli oce ne rocks into as rar east as Puketiti Station (Kenny 1984b; Mazengarb the Tolaga Group (Early Miocene to Late Miocene; ef a l. 199Ia). The southernmost known Ihungia Waitakian to lateTongaporutuan) and the unconformabl y conglomerate is at Whatatutu (Y17/30403 1) although overl ying Mangaheia Group (latest Mi ocene to Early coarse-grai ned sandstone prese nt as far south west as Pliocene; late Tongaporutuan to Opoitian). Otoko (X I7/178927) is a probable di stal eqoivalent. Locall y, th e conglomerate is present over an area Early Miocene ex tensi ve enough to show on th e 1: 250 000 map. Conglomerate beds are channelised and range up to about Ln northern most Raukumara Peninsula the Matakaoa 10m thi ck. They are common ly interbedded with dark Volcani cs are overlain un conformably by the Whakai grey, fine- to coarse-grained sa ndstone and intercalated Formation (Chapman-Smith & Grant-Macki e 197 1), the wi th mud stone or altern atin g sand stone and mudstone basal bedsof which are limestone-cemented brecc ia with fac ies. Clasts are typicall y well rounded pebbles and intercalated, naggy, oyster-ri ch limestone (Fig. 23, Mlb). cobbles of igneous lithologies, but there are also well Most of the Whakai Formation consists of well bedded, rounded boulders (as at Tarndale Road, Y16/3 1I 121 ). alternating sa ndstone and mudstone, mass ive mudstone Igneousand metamorphic clast typesinclude hornbl ende­ (Fig. 24, Mlm) and metre-bedded lensoidal bod ies of ri ch gneiss, gabb ro, hornbl end e gabbro, quartz-ri ch igneous pebble conglomerate (MIc) of Early Miocene tonalite, hornbl end e horn fels tran sitional to hornblend e (Otaian-A ltonian) age. In the Tauwhareparae area units schi st, qUaJ1Z diorite and granodiorite (W.A. Watters in of Late Oli gocene to Early Mi ocene (Waitakian-Otaian) M azengarb ef al. 199 1a). Sedimentary clasts in clude tuffaceous sa ndstone-mudstone and brecc ia­ concretions, grey chen , reworked mac rofoss il s and , conglomerate were formerl y included in the Mangatu locall y, rafts of intraformational siltstone up to 2.5 m Group (Mazengarb e1 al. 199 1a) but are now recogni sed acros s. Some of the igneous clasts are deri ved from as part of the Tolaga Group (Mlb & Mlv). The breccia Matakaoa Volcanics but th e oth er so urces are still incl udes large bloc ks of Tai tai Sandstone and Whangai unknown. Formation, and rounded cobbles and pebbles of basalt and gabbro. At Huiarua, near the head waters ofthe Mata Sedimentary breccia/conglomerate beds (both rounded River (y 16/4203 08), sandy and muddy limestone with and angular clas ts) are present throughout the Tolaga basal brecc ia-conglomerate and intercalati ons ofbreccia Group (differenti ated locall y, Mlb), but are most common (Mil) rest un conform abl y onTikihore Formati on. These in the lower part (Mazengarb el al. 1991 a). The thi ckest breccia-bearing units are considered to be synorogenic, and coarses t are northeast of Paraeroa Stream deposited in "piggy-back" basinsduring and immedi ately (Y 16/567357); finer grai ned equi va lents are present near foll owing emplacement ofthe East CoastAllochth on.The th e Ri ver (X 17/198978) and in a fault sliver in wide ran ge of litholog ies prese nt in so me brecc ias Hihiroa Stream (X 17/1909 12). Indi vidual breccial indicates East CoastAll ochth on units were being uplifted conglomerate beds are up to 30 m thick.Clasts are derived and eroded during the thrust sheet emplacement. mainly from the sedimentary roc ks of the East Coast A lloc hthon.C lasts over a metre across are rare, lhough The bulk of the Tolaga Group (MI) compri ses massive th e largest known is a 40 m x 7 m block of Whangai and thinly bedded mudstones. The typi cal massive mudstone (Mazengarb el al. 1991 b). mudstone ismoderately soft to moderately hard, medium grey in co lour and sli ghtly calcareous, with scattered Glauconitic sand stone (Whangara Sandstone, Mlw; calcareous nodules and concretion s, intercalated beds of Neef & Boltri ll 1992) at the base of the Earl y Mi ocene is fine-grained sandstone and tuff, and rare macrofossils here incorporated in Tolaga Group. The un it has been (small bi valves and gastropods). Microfossils, soch as differentiated onl y in so me areas (e.g. near Whangara, foraminifera, are co mmon throughout and are the Y18/660790). It comprises up to 20 m of medium- to principal means of dating th e rocks. Centimetre-bedded coarse-grained, hi ghly glauconilic sand stone. Several and - laminated mudstones are simi lar small areas of limestone are mapped separately (Mlk). lithologica lly and are a transitiona l facies into altern ating In the upper Waipaoa vall ey the Moonlight Limestone centimetrc- to metre-bedded sandstone and mud stone. In consists of up to 150 m of moderately to well cemented, the area of the Raukumara map th eTolaga Group isup to poorly bedded, locally naggy, coarse- to very coarse-

27 Figure 23 On the point separating Hicks Bay from Onepoto Bay (Z14/772875) the Matakaoa Volcanics (dark beds on right) are unconformably overlain by Early Miocene breccia and limestone of the Whakai Formation, Tolaga Group. The contact is irregular and large blocks of Matakaoa basalt are present as clasts (e.g. bottom left). The Talaga Group rocks were deposited in shallow water and have subsequently been uplifted and tilted to the southeast (left). Photo CN42422/9: D.L. Homer

28 Figure 24 Gently dipping mudstone of the Early Miocene Whakai Formation beside State Highway 35 near Hicks Bay (214f778874) is the prevalent lithology wi th in the Tolaga Group. The thin , brown-stai ned sandstone beds define bedding and show that the fractured appea rance of the mudstone is a surface effect resulting from wetting and drying cycles. A sma ll fault dips toward the person. Photo CN42200119: DL Homer

grained, bioclastic limestone interbedded with calcareous mudstone, minor sa ndstone, and iI1lervals of ahernating sand stones. Large oy ster shell s are common . The we ll bedded sandstone and mudstone (MI ). Altern ating Kouetumarae Limestone isan equi valent present locall y sandstone and mud stone un its are locally distin gui shed between the lower M ata Ri ver and Ihu ngia River; it (Mia). Near Wharekopae, Savell a ( 1992) mapped two consists ofup to 20 m of poorly bedded, fl aggy, bryozoan (in formal) unitsof centimetre- to decimetre-bedded , fi ne­ coquina lim estone and shelly, bryozoan-ri ch sa ndstone . to medium-grained sandstone and mudstone, namely hi s The limestones are shallow mari ne deposit s, inferred to Cocos fl ysch (whi ch includes fossil coconuts; Ballance ha ve accumul ated at shelf depths (Kenny 1984b; el al. 1981) and Rere sandstone. In the vici nity of the Mazengarb el al. J99 1a; Field, Uruski el al. 1997). Mokon ui orangi Range the Cocos fl ysch and overl yin g mudstone pinch out westward ben eath theoverlying Rere So uth west of Rakauroa and Te Karaka the Talaga Group sa ndstone, rocks fo rm bluffs and spectacular southeast-facin g dip slopes along the northwestel11 margin of Mioceneoutcrop, Middle and Late Miocene At Hangaroa River and Mutuera Stream the basal sediments incl ude a thjn conglomerate, cross-bedded, Near Raukokore Torlesse co mposite ten'ane basemen tand shell y, pebbly sandstone (Joass 1987) and muddy rocks of the Eas t Coa st A lloc hthon are overlain fo ss il iferoussand stone of late Earl y Miocene (Altonian) un co nfo rmabl y by Middle Miocene To laga Group age (M.ls). The more ty pical facies are bedded calcareous conglomerate, sandsto ne, mud sto ne and limes tone (l\tOh ;

29 Moore 1957). carTe Puia Middle Mi ocene sedimentary Bay slightl y younger unitsof similar alternating sandstone rocks unconformably overlie Tikihore and Whangai and mudstone have been mapped informall y as Makaretu formations of the East Coast All ochthon (i. e. Early sand stone or Rerepe sandstone (Mia ; Francis 1993b; Miocene beds are absent). In these areas the Middle Field, Uruski el "I. 1997) of late Midd le Miocene Miocene beds are generally less th an 100 mthick. Much (Waiauan) age. thicker Middle Miocene beds are present further south. South ofTe Puia th ey are mainly mudstone, locall y with Betwee n Te Puia and Wairoa Middle Miocene rocks are intercalations of metre-bedded sed imen tary breccia and typically overlain conformably by similar beds of Late lenses of Bexhaven Limestone up to 10 m thi ck and Miocene age, although locall y the relatio nship is 400 m long (Mazengarb el "I. 199 1a). The Bexhaven unconformable. Mudstone is the dominant lithology (MI) Limes tone is a micritic, sulphurous and foss iliferous with interca lations of well bedded alternating sandstone limestone considered to ha ve famled around cold water and mudstone (Mia; Fi g. 25), and shell y muddy sandstone seepson the sea fl oor, simiJ ar to the modern seepsknown (M lz). Late Miocene sandstone-dominated alternating offshore (Lewis & Marshall 1996; Campbell el "f. 1999) . sandstone and mudstone un its present between Gisborne Locall y, however, th e Middle Mi ocene beds are mainly and Wairoa have been mapped as M akaretu sand stone alternating, centimetre- todecimetre-bedded, fine-grained (e.g. Davies el (II. 1998). Beyond the Raukumara map sandstone an d mudsto ne, with minor pebble bou ndary Makaretu sandstone is up to 400 m thick: it is conglomerate. Southwest ofRakauroa- Makarori one such interpreted as a base-or-slope sequence co mprising four unit, the Thnanni Formation (MIn). is up to 2000 m principal turbidite lobes (Davies el (II. 1998; Fig. 26). thick (Field, Uruski el "I. 1997). In north ern Hawke's Some of the Late Miocene seq uences include abundant

Figure 25 This road cut on State Hig hway 35 south of Tolaga Bay (Z1 71705948) provides excellent exposure of Late Miocene Tolaga Group sandstones which are offset by several smali laults. Photo CN42197/13: DL Homer

30 volcanic tuff (MJv) deri ved from rhyolitic eruptio ns in unconformable. Shell y li mestone (Mil) present over a the Coromandel Peni nsula area (S han eer al. 1998). There small area aLTirihaua Station (Y 18/586275) is similar to are excell ent exposures of sandstones ri ch in vo lcanic the slightly old er Bexhaven Limestone and a simil ar delritus at Mah ia and at Gable End Foreland (Fig. 27; origin is inferred. also back cover). Decimetre- to metre-bedded, fine­ grained, fossiliferous sandstones which form a prominent Latest Miocene and Pliocene tableland in Mangatu Forest (Areoma Sandstone, Mlr) unconformably overli e Middle Miocene rocks The latest Miocene to Pliocene Mangahcia G roup (Mazengarb et al. 1991 a). A ridge·formi ng unit of Late (Mazengarb er al. 1991 a) consists of up Lo 2000 10 of Miocene fossiliferous sandy mudstone is present along shell y sandstone, sandstone and mudstone. It covers large the north coast ofTolaga Bay. Near discon tin uous areas south of Whangaparaoa and in th e vicini ty of East outcrops of shell y limestone 10-20 m thi ck (patutahi Cape, and is present between Tauwhareparae and Te Limestone, Mlp; Beu 1995; Fig. 28) are present with in Karaka (mai nl y in broad sy nclines). withi n the Wa iroa mudstone and th e basal contact may be partly or wholl y Syncl ine and in the western part of Mahia Pen insul a.

Figure 26 Late Miocene Makaretu Sandstone forms prominent bluffs and spectacular dip slopes; it has potential as a hydrocarbon reservoir lithology in the Wairoa area. Pliocene limestone forms a scarp on the horizon at the extreme right (Whakapunake). The hummocky surface on the dip slope results from slumping.The view is towards the south. Photo CN42107/19: 0.L. Homer

31 In northern Raukumara Peninsula th e East Coast mainly ofaltern ating sandstone and mudstone, with lesser Allochthon and Tolaga Group un its are unconform ab ly sand stone, mudstone, tuff and limestone (M azengarb et overl ain by a shallow mari ne sequ ence of tu ffaceous, al. 199 1a; Field, Uru ski el a/. 1997). The basal contact is foss iliferous sandstone, ca lcareous mud sLOne and mi nor conformable in the Tau w hareparae area but limestone (Te Kahi ka Formation of Chapman-Smi th & unconform able in land fro m Gisborne.In pl aces mass ive Grant-Mackie 197 1). Near East Cape the rocks comprise sandstone units are di fferenti ated (Pms). The Ormond an up wards-coarse ni ng and shal low ing seq uence L imestone (Pmm) is known from near Gisborne, at deposited at depths between upper bathyal to shelf . Waerengaokuri and in the low hills betwee n (Ball ance el a /. 1984). Between Te Puia and Tolaga Bay there and Poverty Bay (Beu 1995; Field, Uruski el al. the Tolaga Group beds are un conformably overl ain by 1997). bluff-forming shelly sandstone and muddy sandstone of the Tokomaru Sandstone (Mmk) whi ch is locall y up to South ofGisbome Early Pl iocene Mangaheia Group rocks 500 m thick (B 10m 1982, 1984; Mazengarb el al. 199 1a). are mainly sandstones, some of which are tuffaceous The overl ying R amanui Formation (Pmz) consists (Pms), and mudstone ( Pmz). Several unconformi ty-

Figure 27 Near-vertical , Late Miocene Tolaga Group altern ati ng sandstones (white beds) and mudstones are well exposed in the sea cliffs at Gable End Foreland (Z 17n13836), so named by Captain James Cook because of the prominent white gable-shaped bed .The sandstones contain abu ndant volcanic ash probably derived from contemporaneous volcanic eruptions in th e Coromandel Peni nsula area. The view is towards the southeast. Photo CN12914A: D.L. Homer

32 based, di scontinuous, shelly lim estones have been Melange diffe rentiated (Opoiti Limestone, Pmo a nd Whakapunake Limestone, Pmw; Be u 1995). The Opoiti Areas ofseverely cru shed, mi xed lith ologies are mapped Limestone grades laterally into sandstone on both limbs as melange (mel). Typicall y, fragments and blocks of of the Wairoa Sy ncline (Beu 1995). The unconfo rmably Whangai Formation and Mangatu Group liLhol ogies are overly in g Late Pli ocene shell y limestone (Tahaenui present in a sheared, smectitic mudstone matrix. The Limestone, Pmt; Beu 1995) is co nform ably a nd melange is associated with rocks of the East Coast gradational ly overlain by thick sandstone, mudstone and Allochthon and is also present in the cores of diapiric mjnor limestone. The Pliocene sequence shows marked structures bounded by Neogene rocks, i.e. it has lithofacies and thic kness va ri ati on laterall y, wi th apparentl y been formed by at least two differe nt considerable onlap against pre-existing structures (see mechani sms in two main periods. The presence of cross sections). melange is commonly indicated by areas of slumping.

Figure 28 Late Miocene Tolaga Group Patutahi Limestone (upper, mainly dark layer) is a valuable sou rce of aggregate near Gisborne. This outcrop (X18/223679) near the Waerengaokuri Quarry shows the limestone resting with angular unconformity on well bedded sandstone and mudstone (Middle Miocene Tolaga Group). The limestone face is about 10 m high. Photo CN4219312: D.L. Homer

33 QUATER ARY SEDIMENTS Coleman 1999a, 1999b). The sequences unconfornlably overlie Talaga and Mangaheia groups and have a wide Sediments deposited in Quaternary time (within the last range of lithologies. Mangmuna Fom13tion isstructurall y 1.8 million years) are present in ons hore coastal plain s, simple, generally dipping at less than 5° over large areas, allu vial plains, swamps, alluvial fans and landslides, They although close to some faultsMangatun a Formation dips are described according to their lithology, orig in s. known at up to 20". or inferred age and, for some. their geographic location. Ages are given in termsof the oxygen isotope time scale NOlth ofOrmond the Mangatu na Formation incl udesfine­ (Imbrie ef al. 1984; Crampton ef af. 1995), except th at grained sand , laminated mu d, peat, tep hra and diatomite some deposi ts (e.g. the Ma ngatuna Formation) cover a at elevat ions of up 1.0 150 m above the Waipaoa River wide age ran ge and are mapped as undifferentiated (Figs. 29,30). The muds are fossilifero us and include Quaternary sediments. bi va lves (e.g. Hyridel/fl , a fresh water mu ssel), gastropods, fi sh skeleton s. moa bones and impress ion s Pleistocene sediments of the Waipaoa catchment of feathers and leaves (Hill 1889: Oli ver 1928).

Up to 150 III of Pleistocene sedi ments are present in the The three members differentiated in th e Gisborne­ Waipaoa Ri ver catchm ent between What3tutu and Waihirere area (Neef ef al. 1996) cannot be shown Gisbome. and in outliers at Tirihaua, Waim3ta valley and se parat ely on a map of this sca le. Stratigraphic Pouawa (Mangatuna Formation, eQa: eefef ai, 1996; relationships are more complex th an outlined by Neef

Figure 29 Flat-topped hills adjacent to the Waipaoa River at Kaitaratahi (middle ground, Y17/374867) are formed of Mangatuna Formation lake deposits about 100 m thick. The lake in which they accumulated occupied a large area in the middle and lower part of the Waipaoa catchment in Early Pleistocene ti me. The base of the fo rm ation is exposed on the river bank at the left . The view is towards the east; the distant hills are mainly of Pliocene Mangaheia Group rocks . Photo CN42318/8: D.L. Homer

34 Figure 30 Alternating, well bedded, very fine sand and clay of Mangatuna Formation lake deposits at Aangatira Station, Te Karaka (Y171 326950). Clay beds infill ripples preserved at the tops of sands. The red and wh ite divisions on the scale are each 10 long.

(Coleman 1999b). The Calhome Member compri ses Mangatuna Formati on containsa number of pumiceou s mainly weakly indurated mud ston e with intercalated tephras and/o r di stal ignimbrites, the products of large tephras, ignimbrite. paleosolsand minor gravels.A basal sca le volcanic eruption s in the Taupo Volcani c Zone, lignite 3 In thi ck is present near Mangatuna Station 150 km to the west. A 3 III thi ck tephra near the base of (Y 18/482750). The MalOkitoki Member is mainly iron­ the Mangatun3 Formation in the area of Gi sborne city is stain ed, matri x-supported, cross-bedded , polymict gravel co rrelat ed with th e I Ma old PoLaka Ignimbri te with interca lated lenses of sa nd which locally, as at (synonymous with tephra, Coleman I999a, 1999b; Hitchens Quarry (Y 18/455748), contains abundant Shane 1994). A near-basal. 8 m thi ck tephra at Te Karaka nonmarine fo ssil s. Clasts are derived from a vari ety of ha s be en dated by the fi ss ion track method at Cretaceous and Terti ary rock s, with a large co mponent 620000 ± 6000 years B.P.(B.Y. Alloway pers. comm . from Torlesse composite terrane basement (Neef et al. 1999). A poorly known estu arine facies present at Kaiti 1996), and igneo us clasts id entica l to those in Early Hill co ntai ns th e subtropical bivalve Alladara ,rape~ia Miocene Talaga Group conglomerate, indicating the and is. apparentl y, significantly younger ( 120 000 years so urces were 11 01111 ofWhataltllll .Th e Town Hill Member B.P. ; Brown 1995). includes grey and blue-grey clays, pebbly sandslOnes, fossil -rich horizons up to 1.5 111 thick and thin tephras. The fo ss ils (e.g. Austrovenl/s stllfchburyi) indicate deposition in estuarine environments.

35 Shallow marine sediments near Cape Runaway are as old as c. 9000 years B.P. and lie up to 12 m above present sea level (Pullar & Penhale 1970; Pullar & Warren Shallow marine, fossilifero us, pumiceous, sa nd y 1968).Comemporaneous uplift of the eastern side of mudstone and sandstone (Q9m) present between Cape Poverty Bay is responsible fo r the progressive decrease Runaway and Te Araroa were previously correlated with in elevat ion from the oldest dunes to the coast. Estuarine what is now known as Mangatuna Formation at Gisborne and swamp deposits (Qla) are present behind the modern (see Adams 19 10; Chapman-Smith & Grant-Macki e beach ridge and foredunes, and in the swales of older 197 1). Fission track daLin g of intercalated tephras (D. beach ridges. They are typicall y present near the mouths Seward ill Sumosusastro 1983; Beu et at. 1990) indicated of ri vers and streams and are well developed on the an age of about 220 000 years B.P. However, earl y Poverty Bay flats. In contrast to the sand-dominated generation fission track ages have been found to be too Poverty Bay system, the beach ridges at Te Araroa are young (Seward 1979) and an age of Oxygen Isotope Stage mainly gravel (Garrick 1979), reflecting the nature of 9 (c. 320000 years B.P.) is considered more li kely (L.J . the sediment supplied by th e adjacent Karakatuwhero Brown pel's. camm.). The older age is consistent with River. the greater deformation of th e unit (as expressed by elevation changes outl ined below) compared with the In Holocene time (overthe last 10000 years) beach dunes adjacent Q7b mari ne terrace at Malakaoa Point. and sands about 20 m thick have accumulated to form a tombolo between bedrock highs at Opoutama and Mahi a The Te Piki Member outcrops between 27 m and 60 m (Cameron 1999). Sand dunes and gravel beach ridges above sea level at Te Piki 3 km ESE of Whangaparaoa. between Wairoa and uh aka are present as a continuous It is up to 35 m thick and contains a ri ch and di verse strip about 23 km long and up to I kill wide. The gravel molluscan fauna indicati ve of shall ow marin e deposition has a hi gh proportion ofTorl essecomposite terrane clasts in conditions slightl y warmer th an th e present day. The which were probably transported down the Wairoa and Maddox Member is an estuari ne equivalent present over ri vcrs before coastal processes transported them a small area at YI4/658877, 12 km ESE of Te Pi ki. It to thei r present position. T hese deposits are a partial could mark the inl and extent of the mari ne incursion, or barrier to drain age oflocal streams into the sea and control a lte rn atively, a seaway may have c onnected the presence of several shallow lakes and lagoons (e.g. Whangaparaoa and Hi cks Bay. It is present at up to Whakaki Lagoon). and the accumulation of estuarine and 2 10 m above sea level, indicating differential uplift flu vial deposits (Fi g. 8; Ota et at. 1989). (Chapman-Smith & Grant-Macki e 197 1). Rates ofcoastal accreti on or erosion vary widely within Marine terraces the ma pped area (G ibb 198 1). Ota et at. ( 1989) demonstrated that the Wairoa-Nuhaka coastal plain Elevated marine terraces (Qlh, Q3b, Q Sb, Q6b, Q7b, formed over the last 9000 years, prior to which the Q9b, Qllb) are common in many coastal areas, notably shoreline was c. 2 km landward of the presenl position. al ong the Bay of Plenty coast between Opotiki and East Brown ( 1995) estimated that at about 7500-5500 years Cape, and at Mahia Peninsul a (Fig. 9). The terraces B.P. the Holocene shoreline in Poverty Bay lay 15 km represent erosion surfaces cut in bedrock by marine in land. The associated marine and nearshore deposits processes and subsequently raised by tectoni c uplift to have subsequently been buried by alluvi um fro m the as much as 300 m above present sea level. The terraces Waipaoa Ri ver. are commonl y overlain by thin deposits of gravel and sand, in places containing shallow marine fossil s. Terraces All uvial terrace and fl oodplain deposits and terrace deposits may be capped by younger tephras and loess (Fi g. 3 1), and by other younger nonmari ne Allu vial gravels, muds and minor sand deposits (Qla , deposits (Berryman 1993a, I993b). Near Opotiki terrace Q2a, Q3a, Q4a, QSa) are widespread in all th e major remnants al 20 10 100 m above sea level are c. 400 000 catchments. A llu vial terraces (Figs. 6, 32) represent years old (QI Ib; Manning 1996). At Te Araroa a terrace remnants offormer river levels and, typicall y, are mantled surface 300 m above present day sea level (Q5b) is by tephras deri ved from eru ptions in the Taupo Volcani c c. 125 000 years old (Yoshi kawa 1988). Zone. Those older th an about 20 000 years may also have a thin covering of loess. Alluvial terraces occur up to Coasta l plain deposits 300 m above the adjacent modern ri ver beds (as in the headwaters of Mata Ri ver at Y 16/486256). In most areas Coastal plai n deposits cover a minor part of the mapped they are poorly dated (OLa et a/. 1985; Yoshikawa eI a/. area. Much of Gisborn e City is built on the 1988; Mazengarb eI al. 199 1a; Berryman el at. 2000). Sands, a un it of beach and minor dune sands (Q l b) T he main exception is the sequence of lerraces in th e present as a series of ridges and swales (troughs). They middle reaches of the Wa ipaoa River between Kaitaratahi

36 Figure 31 Thick tephras present in the upper part of the sea cliff at Awaawakino Bay (X15/993497) are the products of eruptions in the Taupo Volcanic Zone ; here they are as old as 300 000 years. The lower part of the exposure is of older, undated fluvial (river or stream) deposits. Photo CN4228613: D.L. Homer

and Whatatutu. Here, the highest of the four terrace sets Alluvial fans is 120 m above the adjacent river level (Fig. 6) and 90000- I 10000 years old. The terraces are aggradation Allu vial fans present at the mouths of some steep, rapidly surfaces formed duri ng periods of cool climate when erod ing gu lli es lypically consist ofpooriy soned angular retreat of the tree line facilitated hi gher rates of eros ion gravel (Qla. Q3a. Q5a): some are mantled with tephra in the headwaters of the catch ment. During warm periods and loess. During "normal" cl imate regimes water flow protective forest cover was re-established and the river is confined to incised channels, but during rainstorms continued downcutting in response to tectonic uplift these are overwhelmed and material is deposited over a (Berryman e1 al. 2(00). wide area, as at Tarndale gu lly (Fig. 33). The fan at the mouth oftheTarndale gull y tributary periodically blocks The Poverty Bay fl ats are the most extensive and best theTe Weraroa Stream during intense rainstorms, creatin g studied allu vial noodplains in the mapped area (Pullar a temporary lake behind the fan debris. 1962; Pu ll ar & Penhale 1970; Brown 1995). They are underiain by up to 200 m of mainly nuvial silLS with minor Landslides interbedded gravel layers which, locall y, inc lude up to 60 mof estuarine or shallow marine sand and mud present Landslides are di sc ussed in more detail in the secti on on near the top of the sequence. Gravel-filled channels up Geological Hazards. For some landslides onl y th e to 15 m thi ck were deposited 9000 - 12 000 years ago head scarpsare shown, but for ot hers an overpri nt pattern (e.g. th e Makauri gra vel; Brown 1995). is lI sed to show th e area involved. Where displacemen t

37 Fig ure 32 Wharekia (1 106 m, Yl51588566), on the south side of the Tapuaeroa valley, is one of several spectacular sandstone peaks in this catchment. Wharekia, and the adjacent mountains Aorangi andTaitai, are formed of erosion·resistant sandstone bodies surrounded by Mokoiwi Formation.Two terrace surfaces at 400 m and 300 m elevation (arrowed) , and approximately 30 000 and 20 000 years old respectively, illustrate the speed at which downcutting (and erosion) is occurring in this valley (approximately 8 mml year). GUlly erosion in the Mokoiwi Formation (left middle ground) is contributing to the rapid aggradation of the Tapuaeroa River bed (left foreground ). The river bed here is about 150 m above sea level. Photo CN42280111: D.L. Homer

issign ificant , and there is substantial mod ification ofthe 1945). The sinter covers an area 600 m long and up to 20 bedrock, ule lands lide deposits are mapped separately m wide that is restricted mainl y to an east-west ori ented (QlI). The largest of the onland landslides is the 18 km' fi ssure, possibly formed by movement on the Te Puia Landslide (Fig. 34) formed c. 6 500 years ago Landslide. The age of the upstandin g sinter ma ss is (Howorth & Ross 1981 ). Small lakes and ponds are unknown, whereas sinter deposits are currently forming present on so me landslide surfaces (as at Ti ni roto). nearby at the hot springs (see below). The elevated Undifferentiated lake deposits oftheWaerengaokuri area po sition of the sinter is a result of erosion of the (e.g. Bishop 1968b) may have been deposited behind surroundi ng (and softer) bedrock. landslide-formed dams across the Hangaroa River.

Te Puia sinter

At Te Puia Springs (Z 16/754357, Fig. 35) calcareous sinter (Qcs) deposited from hot min erali sed water cooling aLor near thegroun d surface has formed anelongate mass ri si ng up to 30 m above the local reli ef (Mac ph erson

38 /

/

Figure 33 This view is towards the northwest across Te Weraroa Stream to the Tarndale slip, Mangatu Forest (foreground, Y16/302172). During heavy rainfalls, debris (Whangai Formation) from the slip and gully is transported downstream to be deposited as an alluvial fan at the junction with the Te Weraroa; occasionally the stream is blocked temporarily. This gully is insignificant in terms of the area of the Waipaoa catchment yet it generates 2-3% of the current annual sediment load of the Waipaoa River (DeRose et a/. 1998). The pine plantation has slowed the growth of the gully and is serving to protect other steep gullies from eroding in this manner. Photo CN42414115: D. L. Homer

39 Figure 34 The Tiniroto Landslide (outlined, X18/040600) formed within mudstone of Pliocene age on a gently dipping bedding plane inclined towards the Hangaroa River. The initial failure and subsequent movements may have been triggered by earthquakes, but the downcu«ing action of the river serves to continually destabilise the toe of the landslide. The bush-covered dip slope and scarp at top right are formed by the Whakapunake andTahaenui limestones. The view is towards the southeast. Photo CN41 020111: D.L. Homer

Figure 35 At Te Puia an ancient sinter (hot spring deposit) towers over modern hot springs. Newly formed sinter is present beside the person. Photo CN42 168/25: D.L. Homer

40 TECTONIC HISTORY

Early and Late Cretaceous SSW-directed subduction of the oceanic (Pacifi c) plate beneath th e continental margin (Australi an Plate). The The Torlesse compos ite terrane and oth er Eastern Late Cretaceous to Oli gocene passive margin sequence, Provin ce terranes are considered to have been juxtaposed which had accumulated east and north of Raukumara at a convergent continental margin on the edge of th e Peninsul a, was di smembered into a seri es of thrust sheets Gondwana supercontinent before the end of the Earl y and emplaced sequentia ll y over the in-place equi valent Cretaceous (Bishop er al. 1985; Adams & Kell ey 1998). sequences. In places the rocks ofthe all ochthon have been Ln western Raukumara Peninsula the Torlesse rocks were sheared and mi xed together, forming broken formation li thi fied, deformed, up li fted , eroded and th en buried and melange. Obduction ofthe East Coast and North land beneath transgressive marine sedi ments (Matawai Group) all ochthons has juxtaposed rocks whi ch were originall y in Early Cretaceous ti me. Matawai Group sediments were deposited far apart from each othe r. In some areas older, deposited mainly in outer shelf or slope env ironments, distal rocks (such as the Matakaoa Vo lcanics and the but the easternmost Matawai Group unit (Waitahaia correlative Tangi hua Complex) have been thrust over Formatio n) accumu lated in a deep marine turbidite fan. youn ger beds (I saac er al. 1994; Rait 2000a). In Raukumara Pe ninsula, and perhaps e lsewhe re, subduction-related deformation (i ncluding thrust fau lting) Most ofthe thrust faults dip nonh to nOltheast and indicate may have continued throughout Early Cretaceous time SSW-di rected emplacement, but in some areas they dip and in to the Late Cretaceous (Mazengarb & Harris 1994). southwest and nOlth. Near the mouth of the Raukokore River Torlesse rocks are thru st over younger Tikihore Mid and Late Cretaceous sedimentary rocks now present Form ation along the southwest-dippin g RaukokoreThrust within the East Coast Allochthon represent deeper water (Fig. 5). South- to nOith-directed imbrication ofTi kihore fa cies th an those of th e correlati ve in -place rocks and are Formati on is also recognised at Orete Point. Torlesse inferred to have ori gin all y accumulated in more di stal rocks forming th e summit of Hikurangi are considered (oceanic) settings. The Matakaoa Volcan ics are in ferred to be a klippe, or outli er, thrust over the underlying and to have accumulated in a di stant , oceanic setting, as part youngerWai tahaia Formation (a parti aJreturn to theTaitai of an oceanic plateau associated wi th a mid-ocean ridge Ove rthrust hypothesis of Wa shburne 1926). The (Mortimer & Parkinson 1996). northeast- to north-directed thrusting is interp reted as backthrusting, perhaps related to reactivation of pre­ Late C retaceous to Oligocene existing thrust faults of Cretaceous age (Rait 1992).

Folding, faulting, upli ft and erosion in Late Cretaceous Thi ck, Early Miocene clastic-dominated sequences time was fo ll owed by renewed marine transgression (Tolaga Group) unconformably overli e the thrust sheets durin g which the basal sandstone un its ofthe Tin ui Group of the East Coast All ochthon, ind icating that the SSW­ were de posited. Late Cretaceous and Paleogene directed obduction ceased in Early Mi ocene time. Pattern s sedimentary rocks of both the in-place and aJ lochthonous of onlap and shifts in th e posit ion of max imum sediment sequences are mainly fine-grai ned and I11ud stone­ accumula ti on indicate differential upli ft a nd domi nated, with intercalated units of deep sea, turbidite submergence, presumed to refl ect deformation associated sandstones (the Tinui and Mangatu groups). They indicate with ongoin g subduction during Middle and Late relative tectonic quiescence a nd low rates of Miocene time; 10caJ unconfonnities are common. Middle sedi mentation, suggesting that during Late Cretaceous and Late Miocene beds include many tu ff beds the source and Paleogene tim e the New Zealand area was a passive of which was probably subduction-related volcanism in cont inental margin . the area of what is now Coromandel Peninsul a.

Miocene to Recent Between Tolaga Bay and Gisborne a series of fo lds and fau lted anti formal structures developed in Late Mi ocene Emplacement ofth e East Coast All ochthon th rust sheets time. The ant iforms are diapi ri c (Stoneley 1962; and depositi on of thick clastic sequences in localised Mazengarb 1998) with cores of Whangai and Wanstead basins in Early Miocene time represent a major change formation mudstones. Some anti forms have cores of in tectonic setting, believed to result from the reacti vation melange. At Huanui Station (Y17/5 18080) the di apiric and propagation of a plate boundary through the region. structure predates deposition of unconformably overl ying The changes in sedimentation rates, depositi onal settings, Early Pliocene rocks. Diapir emplacement is associated sediment type and tectonic style observed at Raukumara with the development of a network of normal faults and Pen in sula match th ose described from Northland (e.g. associated fo lds, commonl y with downthrow to the east Isaac e1at. 1994; Isaac 1996; Rait 2000b). In both areas or south. One such fault is a detachm ent at the base of th ey are inferred to have resulted from south west- to the Tolaga Group between Mangatu Forest and Te Pu ia

41 (Whakoau Fault of Mazengarb el al. 199 1a; Fig. 7). This Aclive faulls and folds late stage normal faulting may be related to gra vity collapse associated with post -Miocene regional uplifL An active fault isoneon which movcment has takcn placc wilhin Ihe last 125000 years. Active faullS are recogni sed In Middle to Late Miocene time differential uplift formed from landforms such as surface traces, fault scarps and a structurall y hi gh area about what is now the Mahia sag ponds (Fig. 36) whi ch are produced when a faull Peninsul a. This high limited the eastern ex tent of th e rupturcs the ground surface (in associati on with a large adjacent sub siding WaiToa Ba sin in whi ch a thick earthquake). Such features are quickly modi fi ed and sequence of sediment s was deposited. Elsewhere, by des troyed by erosion. In the Rallkllmara area the rates of latest Miocene (Kapi tcan) time. shallow marine sediments uplift and eros ion are hi gh and hence few active traces we re bein g deposi ted in many areas and much of the are prcserved. There are al most ce rtain ly far more ac ti ve Raukumara area ha s probably been emerge nt sin ce faulls Ihan the few identified on the map. The known Middle Pli ocene time. Within the last million years a act ive traces are typically short segmenrs, some of which structural hi gh has developed in the area immediately arc assoc iated with major fau lts (for example, the Fernside offshore from Mahia Peninsula (the Lachl an Ridge) with and Pakarae faults). Only Ihe Pakarae Faull has been consequent coseism ic uplift and WNW tilting of marine studied in detail. It has moved a total of 16 m vertically terraces (Berryman 1993b). Uplifl rates at Mahia have in three separat e eve nt s within th e la st 5500 years been variable during Ihe last 180000 years. in the range (Berryman el al. 1992). The effects of aClive faulting on 1-3 mm/year (Berryman 1993b). Elsewhere. dating of drainage are ev ident in several places in the Raukumara terrace deposits has shown that Late Pl eistocene and Range (e.g. near MOIU , X 16/ 120368). Downstream from Holocene uplift rates were as hi gh as 4 mm/year (Ota el the Pakuratahi Fault the M otu and Pakuratahi ri ve rs are al. 1992). Yoshikawa ( 1988) suggested Raukumara deepl y in cised but, in co mrast , the area upstream is Penin sul a is being upwarped a"y mmetri ca ll y as <.l growing characteri sed by ex tensive ri ve r terraces, with small an ticlinal stru cture. Uplift rates are hi gher in the ce ntre remnan tsof lake bed s. At times fa ult movement may have orthe range and where th e ax isof the structure intersects tempo raril y dammed th e rivers. the coast, near Te Araroa. The Mangaone Anlicline (X 19/165370) may be a growing Differential sub sidence is indicated by the thick fold . II deforms middle Pliocene Slrata and is apparenlly Quaternary sequences present in the lowerWaipaoa valley associated with an area of antecedent drainage in the (Brown 1995). while no vertical movement isrecogni sed upper Mangaone Stream (i.e. thegrowing fold isforming in the coastal rcgion near the mouth of the Wairoa Ri ver a barri er to the natural flow of the stream). At least one (Ota el al. 1989). Al Gisbome weslward tilling of Ihe active fault trace on the sa me trend is present nearb y. Mangatuna Formation demonstrates local differential uplift (to the east) and subsidence (Poveny Bay nats) exceed ing 300 m with in the last million years.

Palcomagnctic studiesshow that di fferent part sofeastern New Zealand have been rotated by differcl1l amounts during Neogcnc time. Two paleomagnet ic domai nshave bee n recog ni sed within the Ra ukumara area (Wri ght 1986; Wrighl & Wa lcott 1986; Mumme e 1 al. 1989 ; Thornley 1996). The Raukumara domain (approximately north of Whangara) shows no rotation with respect to the Australian Plate, but the Wairoa domain to the south has apparently been rotaled clockwise by approximately 500. Rotation of thc Wairoa domain may have occurred because it was locked to the Pacific Plate, whereas the Rauk umara domain is decouplcd and more rigidly attached to Ihe Australi an Plate (Reyners & McGinty 1999). The exact position and nature of the boundary between the domai nsare still unknown ; the boundary is not well ex pressed in the surface geology.

42 Figure 36 North ofTolaga Bay differential movement of the active Marau Beach Fault (Z 1617601 13) has ponded the natural drainage forming a swamp along the downlhrown side. View is 10 the easl and the person in the foreground gives scale.

43 GEOLOGICAL RESOURCES

Only the northern pan of the area is covered by a differs from th ose of the Ta upo- area in that they publicali on based on the Geological Resource Map are not deri ved from , or heated by, volcanic sources. The (GERM ) database (Francis et 0/. 199 1). Data fo r lhe chemistry suggeststhe hot water hasbeen ex pelled from so uthern part of the area arc compiled but not published. sedimentary rocks prese nt at depthsof probab ly greater The Raukumara area has few known occ urrences of lhan 3 km. heated by th e Earth's geolh erm al gradienl metallic min erals; Brath waite & Piraj no (1 993) give (approximalely 25"C/km: Stewart e, al. 1990). At Morere details, but a summary is incl uded here. A full assess ment the springs lie on the crest of a dome structure and it is of the oil and gas prospecls has recentl y been publ ished likely th at the water has mi grated to the surface lh rough by Field. Uruski et 01. (1997). permeab le rocks (e.g. sandstones) and along fau lts.

Aggregate Limestone

In the north west good quality aggregates are quarried Limes tonequarried in the Raukumara area isused almost from Torl esse sandstones (e.g. Moulohora Quarry, enti rely for aggregat e, bu t in th e pa st has also bee n X 16/032 157) or extracted fro m Torl esse-derived river and exploited for agricultural lime (Moore & Halton 1985; beach gravels. Koranga Formation sand stone isquarried Francisel al. 199 1). The major quarries are near Gisborne for aggregale near Malawai (X 17/007035). Matakaoa at Huanui (Earl y Miocene), a nd a l Palulahi and Volcanics rocks are a source of moderate quali ty Waere n g~lOkuri (Late Miocene). Pliocene limestone in aggregate in the Cape Runaway - Hi cks Bay area. but lhe Wairoa-Mahia area was quarried prior to 1970. Small may contain abundant zeolite mi neralswhich cause them fa rm quarri es have worked Weber limestone in the to break down readily on weathering. Away from the main M angatu area. The Late Miocene Patutahi Limestone is ranges there are limited so urces of rock suitable for a suitable source of rip-rap for the protection of river aggregate. Near Gisborne th e Late M iocene Patulahi banks and foreshores. Limestone (e.g. X 18/224679) and th e Late Crelaceous­ Pa leocene Whang<:li Fo rm ati on arequarri ed, although the Smectite latter produ ces only poor quality material. Pleistocene grave l is also quarri ed for aggregate near Gisborn e Smectite cl ay isex tracted from asmall quarry in Wanstead (Y 18/455747). as are lerrace gravel deposils nearWairoa Formati on (Eocene) at Parehaka Stati on near Te Karaka (Y 19/927346). Holocene river gravels (Torl esse-derived) (Y 17/486054). A large quant ity is avail able fo r use if and dunes near uhaka (e.g. Y1 7/17 1284) are quarri ed needed (Ker 1969; Gregg & Carlson 197 1). Smectite was for aggregate and sand . once quarried near Whatat utu and un worked areas of smectite are kn own el sewhere (for example at Ru atori a. G roundwater thun gin, Whangara , Waitangi Hill, Nuhaka and Mahi a).

Groundwater isa val uable resource, part icularly because Metallic minerals the Eas t Coas t of New Zeal and is drought -prone. Large volumes are ex tracted from co nfi ned Qu aternary gravel Over anarea of about 1.5 km 2 nearTe Kumi , in a tribu tary aqui fers in Poverty Bay and Wairoa, mainly (Q sustain of Mangahaupapa Stream (Y 15/497684). poorl y bedded intensive cropping. horticulture and vi neyards. Detailed and intense ly sheared sandstones co ntain pods of pyrite stud ies have been publi shed onl y for the Poverty Bay and chalcopyrite, layers of maroon-co loured tu ffand red flats (Brown 1984; Brown & Elmsly 1987; Taylor 1994) chert . Small qu antiti es of copper ore were mined in the where Lh ere are three recogni sed confined gravel aquifers I 920s. Piraj no (1 979) mapped the hOSl rocks as Mokoiwi (Malokitoki , Makauri & Waipaoa) and the unconfi ned Formati on, bu t th ey are now recognised as Torl esse Te Hapara sand aquifer. Ground water qualit y ispoor and comp os ite terrane ba se men t. Mi nor pyri te and treatment is often necessary befo re it is sui table for cha lco pyrite mi nerali sation is present in M atakaoa domestic use or irri gati on. In Lhe Wa iroa Ri ver vall ey Vo lcani cs near Lotti n Point (Pirajno 1980; Rutherfo rd groundwater isextracted mainly from two confined gra vel 1980) and at Mangatulu Stream, Pukemnarll Range (Cody aquifers (Cameron 1999). Groundwater from limestone & Grammer 198 1). No minera lisa ti on of economi c aquifers has yet lo be exploiled. inlerest has been found (Pi rajno 1979. 1980; Brathwaite & Pirajno 1993). Hot springs Oil and gas Hot saline springs al Morere (X 19/254354) and Te Pu ia Springs (Z16n53357) have insufficient flow rale and heal The relati ve ly comm on oil and gas seeps of eastern (45"C & 65"C respecli vely; Hill 1895; Macpherson 1945) Raukum ara Peninsul a attracted the att ention of earl y for purposesother than bathing. Th e ori gin of the waters explorers (Figs. 37, 38). Belween 1872 and 19 13 pils and

44 Figure 37 Active mud volcanoes and seeps in the (Y17/508894) discharge mud, brine and natural gas. The lack of vegetation is typical, presumably because of the high salinity of the fluids.

Figure 38 At Waitangi Station (Y 17/383016) there are a number of aligned, oil-filled ponds and seeps which for over a century have inspired the search for oil. The oil is warm to touch and may have leaked from a breached reservoir within the Tolaga Group.

45 shallow wells were dug in and near th e seeps at The Raukullmra area is co nsidered to have considerable Rotokautuku. Waitangi andTotangi, and theWaingaromi a potenti al for future discoveries (Field. Uruski el 01. 1997; borehole reputedly produced 20-50 barrels of oil a day Frederi ck el 01. 2(00); there is aC li ve ex plorali on bolh before the derrick was deslroyed by lire in 1887. Histories onshore and offshore. a we lls have yet been dri ll ed in of earl y oil and gas explorat ion have bee n given by the offshore area covered by the Raukulllara map; Hawke McLemon (1972, 1976, 1992) and Francis ( 1993c, 1994, Bay- I was drilled just outside the map boundary. 1995). It proved difficult to drill through th e smectitic clays of the Wanstead Formation , whi ch cau sed major delays, cost overru nsand abando nment s. Th ere wa Salso inadequate understanding of th e geology; only a few of the early well s were dri li ed on slruClure. The 1962- 1972 well s ROlokautuku- 1. Te Horo- I andTe Puia- I we re sited on appare nt surface anticl ine features whi ch on drilling were shown 10 pass inlo probable Ihrusl nappes al depth (Field, Uruski el 01. 1997).

The widespread Whangai and Waipawa fo rmati ons are regarded as the best source rocks in the Raukumara area (Field, Uruski el 01. 1997; Rogers el 01. 1999). Though the Wh angai has less total organi c carbon th an the Waipawa Formmion it is much thi cker and is capable of generatin g greater qu antiti es of hydroca rbons. Som e Cretaceous sand stones have fair reservoir pOlential (Te Wera Formati on, Tahora Format ion and , perhap s, the Tikihore and Tapu waeroa formati ons) and these have been the targets of several wells (e.g.Rere- I ). Fracture porosity is present in parts of Whangai Forma tion . Assess men t of Cretaceo us targets is hampered by the present poor und erstand ing of th e distribution and thi ckness of reservoir unils. In 1985-86 Rere- I drilled 4352 m of M iocene to Cretaceous strata and was still in Early Cretaceous Karekare Formali on al tOlal deplh .The primary target reservoir (Tahora Fonnati on) was absent. In so me areas expl orati on is furth er hampered by di fficulties in determining deepstructure beneath the East Coast Allochthon, by a poor understanding of the ori gin of di apiric structures and by the difficulty in obtaining hi gh quality seismic refl ecti on data.

Some Middle and Late Miocene shelf and deep water turbidite sandstones have good reservoir potential (e. g. Lhe Areom a Sand stone, Tokomaru Sandstone, Tunanui Formati on and M akaretu Sandstone). Prospectsdefi ned by surface mappingand seismicsurveys have been driJled in theWairoa- M ahi a area and in 1998 the fi rs t commercial discovery of hyd rocarbons in the East Coast region was made in the Kauhauroa- I well , 10 km nonheasl ofWairoa. The discovery well nowed gas al up to I1.5 MMSCF a day (Mini slry of Commerce 1998); anolh er polenti al commercial di scovery foll owed (Tuhara- I, drilled 10 km eaSI of Wairoa; Frederi ck el 01. 2(00). In the area of the discoveriesthe target reservoir lithologies are Kauhauroa Limestone, an Earl y Miocene bryozo an -domin ated bi oc lasti c limestone kn own only fro m the drillholes , and a Middle Miocene turbidite complex (the Tunanu i Sandstone of Frederi ck el al. 2000).

46 ENGINEERING GEOLOGY

The designers ofengineered structures in the reg ion face unweathered, form steep natural faces (as at Y16/403165) many challenges because of the properties of local rock and they stand well in steep road cuts (e.g. the Tolaga types and the potential impact of natural processes and Bay "gorge", ZI71705946). However, bedding plane events such as earthquakes, landslides, tsunamis. floods, slippage is a recognised failure mechanism where dip erosion and volcanic eruptions. This section, and the one slopes are underclit. Mudstone-dominated lithologies are following, provide a brief overview of rock properties generall y more prone to slipping than sand stones. and significant geological hazards in the area La help Slumping and bedding fai lures are common. Limestone engineers, architects and planners recognise vulnerability is generally a competent rock type, forming bluffs and and minimise risk. More detailed information appropriate dip slopes. However, large bedding plane failures are to specific sites can be obtained from local territorial associated with some undercut limestone dip slopes and authorities and GNS. The background information given rockfalls occur in the vicinity of bluffs. here is not a substitute for proper site investi gations or detai led hazard assessments. Quaternary sediments

Basement rocks Quaternary sediments are loose, weak rocks (or soil s, in engineering terms). tn places they include soft peats and Torlesse composite terrane rocks are strong and variably mud, un consolidated to poorly consolidated sands and jointed, and hard to very hard when unweathered. gravels, and layers of volcanic ash. Because ofthe range Unweathered rock will stand in steep faces (e.g. th e of materials, their generally unconsolidated nature and massive sandstone forming the gorge in th e Motu River variabl e topographic settings, si te-speci fi c studi es are at X 16/022350 was a proposed dam site) but rock strength necessary before any major engineering works are is decreased with increased weathering and/or jointing. undel1aken . The contact between sandstones and mudstones is a signifi cant rock defect and some road cuttings in the Waioeka Gorge shed mllch loose material, particularly where the strata dip at moderate angles towards the road.

Cretaceous to Oligocene sedimentary rocks

These rocks show great lithologic variation and, corresponding ly, a wide range of rock properties. Wanstead Formation and some other units with a hi gh clay conte l1l , in cluding most of the units mapped as melange, are prone to failure by earth now mechanisms. Other formations (e.g. Whangai and Mokoiwi) are typically moderately hard to hard and of moderate strength, but susceptible to gully erosion and slumping, especiall y where the rocks are fractured or crushed as is common within the East Coast All ochthon.

Matakaoa Volcanics

The gabbro, dolerite, basalt and breccia are vari ably sheared, closely to moderately jointed, hard to very hard rocks which stand well in steep faces when fresh or slightly weathered. Where resistant Matakaoa rocks overlie weaker materials erosion can undermine the steep natural fa ces at the margins of the Matakaoa massifs, resulting in landslides.

Miocene and Pliocene rocks

Miocene and Pliocene rocks range froJ11moderately hard to moderately soft depending on lithology, bedding type, cementation and degree ofweathering. Sandstones, where

47 GEOLOGICAL HAZARDS

Volcanic activity living lower in the catchment on the gently sloping floodplains, because the vast amount ofgravel. sand and The Raukumara area is adjacent to the active Taupo mud added to the drainage systems increases the risk and Volcanic Zone (TVZ) where there have been many height of tlood events. Low-lying terrace land of high eruptions before and since human occupation. Volcan.ic value for agriculture can be inundated by gravel, sand ash from TVZ eruptions has raUen over the Raukumara and mud, as occurred duri ng Cyclone Bola in 1988 (Fig. area in the past, and will do so agai n. The thickness of 6; Si ngleton el al. 1989a, I989b; Page el al. 1999). ash-fall at a particular site is influenced by factors such as the volume of material ejected from the volcano, the Major influences on the susceptibili ty of land to erosion force of the eruption, the prevalent win d directio n and include the extent and type of vegetati on cover, rain fa ll the di stance from the volcano. The last major ign imbritic characteristics and slope angle. Geological factors such eruption in ew Zealand was from the Lake Taupo area as rock type (O'Byrne 1967), tectonic uplift and approximately 1860 years ago; it deposited a maximum earthquake shaking are also very important. Rock of SOO mm of ash near , and 100 mm of ash properties with a major influence on erosion susceptibi lity further east nearWhangara (Healy el al. 1964). Eruptions include: of this size have an expecled frequency of 2S00-S000 grain size - sandstone is generally stronger than years (SCOll 1997). Smaller eruptions from Ruapehu, mudstone Egmonl, Taupo, Okataina orWhite Island are much morc degree of cementation - rocks with high amounts frequent. of calcium carbonate (e.g. limestone) or silica are relatively erosion-resistant (see Pearce el at. 1981 ) The area ofthe Raukumara map is likely to receive minor induration - older rocks are generall y harder than falls of volcanic ash every 20-S0 years (Scott 1997). The younger rocks impact wil l vary depending on the th ickness. Even small c lay mi neral content - many mudstones contain eru ptions could have signi fica nt effects. Fa ll ing ash is smecti te clays and break down readily durin g not toxic but it acts as an irritant, affecting eyes and wett ing and dryin g cycles throats. Casualt ies can result fro m secondary effects such fractu res - fractured rock has lower strength than as roof coll apses. Services and facili ties likely to be un fractured rock affected are electricity supply, telecommunications, water crushing - cnlshed rock associated with major faults supply, waste-water, bui ldings and transportation (ai r, and thrusts has low strength road. rail, sea). Pastoral farming, cropping and orientation of bedding surfaces to the land surface horticulture will also be affected to varying degrees. weathering - degree and thickness of the zone of weathering. Erosion Mudstones oflhe Mangatu Group, Mangatuna Formation and, to a lesser extent, Whangai Formation are the most Raukumara Peninsula is ri si ng in response to deformation erosion-prone geological units in the area. Most rocks of associated with subduction processes at the boundary the East Coast Allochth on are also eroding rapidly, the between theAustralian and Pacific plates; the rate ofup li ft major exception being the resistant Matakaoa Volcanics. is variable, ra ngi ng up to about 4 mm/year (ata el at. Miocene and Pli ocene mudstones are extensively eroded 1992). The uplift is counterbalanced by natural erosion in some ca t.chm ents. Pro t.ecti ve planting of exotic forests processes as streams and ri vers remove a vast amount of started al Mangatu in 1960 (Gage & Black 1979) and detritus to th e sea. However, the influence of man has was later extended to cover other rapidly eroding areas. accelerated erosion processes; for example, the removal Reafforestation has substant iall y reduced the rates of or substantial modification of the native vegetation cover erosion and stream aggradation (DeRose 1996). has created major land use problems. Erosion is recognised as a key problem facing the East Coast region Slope instability and landslides (e.g. Taylor 1970). The Mangatu area in the headwaters of the Waipaoa River provided a textbook case study of Slope instability, often resulting in landslides. earth tlows rapid hillside erosion, gullying and stream aggradation and surface creep, is a major problem for roads. railways. following the conversion of native forest to pasture (Fig. bui ldings and other structures, particularly in areas of 33; Cumberland 1947; Allsop 1973; Hicks & Campbell weak orclosely fractured rock. Rocks susceptible to slope 1998; DeRose et al. 1998). Similar problems are present failure underlie much ofthe hill country southeast of the elsewhere (e.g. the Tapuaeroa and Waikura val leys). crest of the Raukumara Range. from Cape Ru naway to Though the most obvious effects of erosion are in th e Wai roa. The ex tent and type oferosion and slope failure headwaters (the "critical headwate rs" of the Taylor are hi ghl y variable, as is soil development. Shall ow­ Report) accelerated erosion also poses problems for those seated soil slips are comm on on steep topography and in

48 stream headwaters (Fig. 39), as are rockfall s from erosion of the landslide toe destabilises 'he slide leading escarpments of limestone and sands tone. Soil slips are to the likelihood of future fai lures. mainly triggered by heavy ra in fall eventssuch as Cyclone Bola in 1988 (Phillips 1988, 1989). Large rotational The Te Pu ia Springs sett lement is located on an active slumps and bedding plane fa ilures are co mmon in areas landslide, measured asmoving 011 average at 55 mm/year of signifi cant stream in cis ionand alongcoasta l headl ands towards the coast (Gibb 1981). The landslide consis's (e.g. Gibb 198 1), p",ticularly where bedding planes or mainly ofLate Cretaceous bedrock sliding as large blocks other form s of rock defect dip down slope. Earth !lows on a slip plane which may bc lu brica tcd by water from and slumps are co mmon in areas where th e rocksconta in th e adj acent springs. Towa rd s the toe the landslide hi gh proportions of clay mi neral s. as in Mangatu Forest, tran sforms into an eanhtl ow. where Zhang el al. ( 1993) demonstrated that earth flow velocities were significantly lower under forestcover than In many in stances it is imposs ible to prevcnt land slides in pasture. from moving. Long term plann ing should aim to identify areas of po tentia l hazard and minimi se the ri sk, for The Ti ni roto Landslide (Fig. 34) is one of several exa mpl e by preven tin g development onor near unstable land sli des on the banks of th e Hangaroa River that have slopes . Only th e largest landslidescall be shown on thi s formed following downcutt ing and subsequent fail ure I :250 000 map. More detailed information is available along bedding planes . The initial failure may have been from the Large Landslides Inventory, a GIS-compatible tri ggered by an earthquake. Movemen t to wa rd the database held by ul e In stitute of Geological & Nuclear Hangaroa River about 6500 yea rs ago created the Sc iences. distinctive hummocky LOpog raphy and theTiniroLO lakes (Howorth & Ross 1981). Continu ing downcutt ing and

Figure 39 Not all erosion in the Raukumara area is related to deep-seated failure of bedrock.This hillside north of State Highway 2 near Nuhaka (X19/133300) suffered extensive surficial erosion (soil slips) during a recent rainstorm. The steepness of the hillside, limited vegetation cover and intensity of rainfall were important contributing factors. The pale slip scars expose bedrock of Pliocene sandy mudstone.

49 Seismoleclonic hazard(by M. Stirlillg & C. Mazellgarb) The intensit y of shaking is also affected by the local Seismicit y in the Raukumara area isan ex press ion ofthe geology. Areas underl ain by "so ft" sediments, such as subducti on of the Pacific Plate benea th the Au stralian the Quaternary deposit s underl ying the lower Wa ipaoa Plale along th e Hikurallgi margin . Earthqu akes recorded va lley. are capable of amplifying seismi c waves by up to by the New Zealand National Seismograph Network (e.g. two MM intensities compared with adjacent areas situated Anderson & Webb 1994) are distributed over a wide depth on more so lid ("sliff') materi al (i.e. pre-Quaternary range and area. However. the vas t majorit y are in a bedrock). In addition. if seismic shak ing is strong westward-dipp ing zone which defines thedowngoing slab (>MM 6) areas contai ning satu rated fi ne-grai ned sands ofthe Pacific Plate (e.g. Reyners & McGinty 1999). The may liq ucfy. creating local sand boi ls. ground fi ssuring. zone is at about 30 km depth beneath th e east coast. subsidence and lateral spreading. Sed iments prone to deepening to about 60 km beneath the Bay of Pl enty coast. liquefacti on are typi ca lly found in coas tal areas an d Further west, beneath the Bay of Pl enty, th e slab zone vall eys underlain by Quaternary deposits. Strong MM dips more steeply and reaches 300 km depth.The focal intensities can also trigger landsli des (inc lu ding in mechanisms of the earthquakes in th e slab zone lend to offshore areas) and tsun ami s(see below). Su rface rupture indicate normal faultingand are, therefore, consistent with on faults will damage and di spl ace structures bu ilt over tensional strain in the downgoing slab ("slab pull"; them. Reyncrs & McGinty 1999) The level of seismicity over Raukumara Peninsul a is Shall ow crustal seismicity in the Rauk um ara area is morc typical for an area of New Zealand adjacent to the widely scatt ered than the deeper seismi ci ty with some Australi an-Pacific pl ate boundary and considerably signi fica nt di fferences in se ismicity rates parall el to and higher th an the seismi city levels for areas located away perpendicul ar to th e plate boundary. Specifically, th e from the plate boundary (e.g. Southland and Northland). number of th rust events at the plale interface increases to Large earthquakes will certai nly occu r in the future with the northeast. Th is is probably due to a dec rease in the consequent casualties and damage to structures in areas deg ree of coupli ng at the plal e interface in th at di rec tion subj ect to strong gro und motion. Th e mean return tim e (Reyners & McGinty 1999). Focal mechanisms for for a MM 7 event has been estimated as 59 years for earthquakes in the up permost part of the AustraJian Pl ate Gi sborne, and fo r a MM 8 event 180 years (S mith 1995; show ex tensional strain ori ented towards the Hikurangi Dellow elal. 1997). Trough. This is probably due to exte ns io n a nd gravitat ional failure of surfic ial rocks uplifted to form Tsunami the Raukum ara Range (see cross-section C). In hi sto ri c times at least seve n tsunami have affected The hi storical record shows that many moderate to large coasta l areas of the Raukumara map area (de Lange & earthquakes have occurred in the reg ion .The Richter sca le Healy 1986; Mazengarb er al. 1997). Typi call y th e (M ) isa meas ure of the energy released at the eart hquake tsunam i ha ve been assoc iated with earthquakes th ough so urce; 30 eve nt s of Ri chter mag nitude M > 5 have in the past so me have been attributed to submarin e occurred in the peri od 1940-97 and 5 events of M>6. 5 in slumping and submarine mud volcani sm (Eiby 1982). In the period 1840-1 997 (including onc M>7 event in 1995). 1947 two tsun ami with wave heights locall y up to 10 m hi gh inundated a part of the coast near Gisbome. A bridge The Modi fi ed Mercall i scale (MM) is a measure of the was damaged and buildings flooded. incl uding the fonner felt intensity at the ground surface. For agivenearthquake Tatapouri Hotel.These tsunami were probabl y generated the felt effect al thesurface will vary dependingon Richter by earthquakes in the adjacent area offshore (Downes el magnitude, focal depth and distance loep icentre. Because al. 2(00). Local ly generated tsunami are cause for greatest seismic waves areatt enuated through th e Ea l1h , deepand co nce rn as wa rn ing ti mes may be very shorl or distal earthquakes will generally ha ve a much lower MM nonex istent. Th eir wa ve heights can be greater th an valu e th an shallow loc al earthquakes of th e sa me tsun ami genera ted by more di sta nt events. Tsunami magnitude. At least 19 felt earthquakes with MM felt generated by di stant eventstake many hours to reach New intensities (see Table I ) of 5 or grealer have occurred Zealand and an international tsun ami moni torin g system since 1840 (Downes 1995). The largest felt earthquake is in place to provide warnings. was the October 6. 19 14 East Cape- I earthquake with MM intensities up to 9. The 1966 Gisborne earthquake caused slight damage to th e city (Hamilton er al. 1969).

50 Table 1 Modified Mercalli Intensity scale (MM) (in part; summarised from Downes 1995).

MM2 Felt by persons at rest, on upper floors or favourably placed. MM 3 Felt indoors; hanging objects may swing, vibration similar to passing of light trucks. MM4 Generally noticed indoors buf nof oufside. Light sleepers may be awakened. Vibration may be likened to passing of heavy traffic. Doors and windows rattle. Walls and frames of bUildings may be heard to creak. MM S Generally felt outside, and by aimost everyone indoors. Most sleepers awakened. A few people alarmed. Some glassware and crockery may be broken. Open doors may swing. MM6 Felt by all. People and animals alarmed. Many run outside. Objects fall from sheives. Glassware and crockery broken. Unstable furniture overturned. Slight damage to some fypes of buildings. A few cases of chimney damage. Loose material may be dislodged from sloping ground. MM7 General alarm. Furniture moves on smooth floors. Unreinforced stone and brick walls crack. Some pre-earthquake code buildings damaged. Roof tiles may be dislodged. Many domestic chimneys broken. Small slides such as falls of sand and gravel banks. Some fine cracks appear in sloping ground. A few instances of liquefaction. MM8 Alarm may approach panic. Steering of cars greafly affecfed. Some serious damage fa pre-eart hquake code masonry buildings. Mosf unreinforced domestic chimneys damaged, many brought down. Monuments and elevated tanks twisted or brought down . Some post-1980 brick veneer dwe ll ings damaged. Houses not secured to foundations may move. Cracks appear on steep slopes and in wet ground. Slides in roadside cutt ings an d unsupported excavations. Small ea rthq uake fountains and other instances of liquefaction. MM9 Ve ry poor quality unreinforced masonry desfroyed. Pre-earthquake code masonry buildings heavily damaged, some collapsing. Damage or distortion to some post-1980 buildings and bridges. Houses not secured to fou ndations shifted off. Brick veneers fall and expose framing. Conspicuous cracking of flat and sloping ground. General iandsliding on sfeep slopes. Liquefaction effects intensified, with large earthquake fou ntains and sand craters. MM 10 Most unreinforced masonry structure destroyed. Many pre-earthquake code buildings destroyed. Many pre-1980 buildings an d bridges seriously damaged. Many post-1980 bUi ldings and bridges moderately damaged or permanently distorted. Widespread cracking of flat and sloping ground. Widespread and severe landsliding on sloping ground. Widespread and severe liquefaction effects.

5 1 AVAILABILITY OF QMAP DATA ACKNOWLEDGMENTS

The geological map accompanying lhis book is derived This map has been compiled fro m previously published from information slored in the geograph ic information and unpublished mapp ing. M aj or sources ofinfomlation system (G IS) database mail1lained by the InslilUte of included unpubli shed 1:50000 compi lations by staff of Geological & Nuclear Sciences and fro m olher GIS­ the former New Zealand Geological Survey, notably work compatible dig ita l dat abases. The data shownon the map by D.A. Francis, C. Mazengarb, P.R. Moore, and I.G . are a subset of the available inform ati on.Customi sed Speden. In particul ar we acknowledge the work of Phil single-factor and mul tifaClar mapscan be generated from M oore who, with and separately from the mapcompilers. the GIS and integrated with other data sets to prod uce, spent many summers collecting data. Field assistance and forexample. maps showi ng fossil ormi neral localities in additional fi eld mapping were provided by J.S. CramplOn, relation to specific rock types.ormaps showing rock types M.J . Isaac, R. Van Di ssen. P. Huber, J. A. Lyall, W. in relati onto the road network . Data can be presented for Win gate and membersof the M aze ngarb famil y. user-defi ned spec ific areas, for irregul ar areas such as loca l authori ty territori es, or in the form of stri p maps The use of in formati on from unpubli shed theses by showing informationwit hin a specified di stance of linear students al the Uni versily ofAuckl and (W. M. Blom, J.L. features such as road s or the coastline. The information Coleman, D.A. Feary, J.D. Gibson, W.G.R. Gifford , P H. can be made availab le at any required sca le bearing in Hm , K. Hoolih an, MJ. Isaac, J.A. Kenny, C. Mazengarb, mind the sca le of data capture and th e generali sati on P.R. Moore, P. RUlherford, R. Savella, C. Webb), Vi ctori a involved in digiLising. M apsprod uced at greater than 1:50 Uni versity of WellinglO n (K.R. Berryman, YJ. Joass. 000 scale will not show acc urate, detai led geolog ical W.R . Moore, GJ. Rait, PJ. Sum osusasu o. S. Thomley. information unless they are based on poi nt data (e.g. I.c. Wright) and Canterbury Uni versily (L. Fergusson) structural infomlation). If required the QMAP series maps is gratefull y ackn owledged . Staff of th e geology canalso be made availabl e in di gi tal fonn using standard departmems are lhanked for their help. data interchange format s. In form at ionon landslides istaken from aerial photograph The di gital data have been captured from data record maps interpretationsand fro m the Large Landslides [nven tory compi led on standard 1:50000 NZMS 260 topograph ic held by lhe In stitule of Geological & Nuclear Sciences. maps. These record maps are fil ed in GNS offices in We thank th e N ati onal Institute for Water and Dunedin and Lower HUll (Gracefi eld) and, although Atmospheri c Research (NIWA) for providing access 10 unpubli shed, are avail able fo r consultation. They are th e bathymetric conlOurs and lhe offshore fa ult dala stored on transparent film and copi es can be made. The developed by lhe FRST-funded AClive Seabed Fealures legend and mapping philosophy used for the detailed programme. lndoPacifi c Energy Lid. andWeslcch Energy mapsare based on lith ostrati graph y and may differ from ( Z) Lid . are lhanked for granling permission to use lheir th ose used on QMAP. con fi dential seismic data to constrai n the cro ss-secti ons.

For new or additional in formation, for pri ntsof thismap J .G. Begg, LM. Lee, and GJ . Rail assisled in map at other sc aJ es, fo r selected data or combi nationsof data compilati on. Developm ent and mai nte nance of th e GIS sets or for deri vati ve or single- factor maps based on database was by D.W. Hero n and M.S. Rattenbury, with QM AP dara, please contact: di gital capture and map producti on ass istance from J.M . Arnst, D.W. Heron, LM. Lee and J.A. Lyall. The map QM AP Leader draws heavil y on published and unpublished paleontology InSlilUle of Geological & uclear Sciences Lid. resullS, particularly on work by A.G. Beu, J.S.Cramplon, P. O. Box 30 368 H.E.G. Morgans,G.H . Scon, I.G. Speden, c.P. Suong Lower HUll and GJ . Wilson.

The map and lex t were reviewed by J.G. Begg, MJ . [saac, M.G. Laird and P.R. Moore.

Fu nding for the project was provided by the Foundati on for Research, Science & Technology conuact C05303 and by the Instilule of Geological & uclear Sciences.

52 REFERENCES

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58 Quennell, A.M. 1939: Geological report on the Kauhaufoa Silberling. NJ.: Nichols. K.M.; Bradshaw, J.D.: Blome, C.D. structllre, Opoiti S.D., Gisborne L.D. New Zealand Oil 1988: Limestone and chert in tectonic blocks from the Esk Exploration Company Ltd. Unpublis hed open-file Head sublerrane, South Isl and. New Zealand. Geological petroleum report 18. Welli ngwl1. Ministry of Economic Society ofAmerica bulletin 100: 12 13-1223. Development. Si ngleton. P.: Trotter. c.; Widdowson, J.; Brenstrum. E.; Brown, Quennel!. A.M. 1940: Geological report on the Wa iroa area, L.J . 1989a: Cyclone Bola I I. Alpha series leaflet 63. Gisborne di strict. New Zealand Oi l Exploration Company We llington. Department of Scientific & Industrial Ltd. Unpublished open-fi le petroleum repo n 19. Research. Wellington. Ministry of Economic Development. Singleton, P. ; Trolle r, c.; Widdowson, L Korte, C. 1989b: Rait, GJ. 1992: Early Miocene thrust tectonics on Raukumara Cyclone Bola 12. A lpha series leaflet 64. Well ington. Peninsul a, northeastern New Zealand. Unpublished Ph.D. Department of Scientifi c & Industrial Research. thesis, Victori a Un iversity ofWell ington, Wellington. New Smith, W.O. 1995: A procedure for modelling near-field Zealand. earthquake intensities. Bulletin of the New Zealand Rait, GJ. 2000a: Amounts and rates of transport of the National Societyfor Earthquake Engineering 28: 218~223. Northland and East Coast a llochthons (abstract). Speden. I.G. 1972a: New fossil localities in the Torlesse Geological Society of New Zealand annual conference, Supergroup, western Raukumara Peninsula, New Zealand. Wellington. Geolog ical Society o f New Zealand New Zealandjoumal ofgeology and geophysics: 433-445. miscellaneous publication 108A: 129. Speden, I. G. 1972b:An o li slOstrome in the Earl y Cretaceous at Rait. GJ . 200Gb: Thrust transport directions in the Northland Oponae-Wairata, Raukumara Peninsula (abstract). P. 21 Allochthon, New Zealand. New Zealalldjollmal ofgeology ill New Zealand Geological Survey ConferenceAbstracts, alld geophysics 43: 271-288. Hastings conference. Wellington. Department ofScientitic Rait, G.; Chanier. F.; Waters, D. 1991: Landward- and seaward­ & Industrial Research. directed th rusti ng accompanying the onset of subduction Speden, I.G. 1975: C retaceous stratigraphy of Raukumara beneath New Zealand. Geology 19: 230-233. Peninsula. part I: Cretaceous stratigraphy of Koranga (parts Rattenbury, M.R.: Heroll, D.W. 1997: Revised procedures and N87 and N88): part 2: geology of the LowerWaimana and specifications fo r the QMAP GIS. Lnstitu te of Geological Waiotahi Valleys (part N78). New Zealand Geological & Nuclear Sciences science report 97/3. Lower Hutl. Survey bull eti n 9 1. Wellington. Department of Scientific Institute of Geological & Nuclear Sciences Ltd. & Industrial Research. Reyners. M.; McGinty, P. 1999: Shallow subduction tectonics Speden, I.G. 1976a: Fossil localities in Torlesse rocks of the in the Raukumara Peninsula, New Zealand. as ill uminated North Island. New Zealand. JOl/mal ofthe Royal Society by earthquake focal mechanics. JOt/mal of geophysical ofNew Zealand 6: 73-91. research, B, solid earth and planets 104: 3025-3034. Speden, I.G. 1976b: Geology of Mt Taitai. Tapuaeroa valley. Ridd, M.F. 1963: The geology of the Whangara-Waimata area Raukulllara Peninsula. New Zealand journal of geology - GR22. BP, Shell & Todd Petroleum Development Ltd. wul geophysics 19: 71-1 19. Unpubli shed open-fil e petroleum report 323. Wel lington. Sporli, K.B. ; Ballance, P.F. 1985: Terrane map, North Island, Ministry of Economic Development. New Zealand (abslract). Geological Society of New Rogers. K.M. ; Collen, J.D.: Johnston, J.H. ; Elgar. N.E. 1999: Zealand annual conference, Christchurch. 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60 This full colour, large format geological map illustrates the geology of Raukumara Peninsula and northern Hawke's Bay (eastern North Island, New Zealand) at ascale of1:250 000. The map is panofa series initiated in 1996 which will cover the whole country.

Onshore geology, offshore bathymetry and geology are shown, derived from published and unpublished mapping by the Institute of Geological & Nuclear Sciences, the National Institute for Water & Atmospheric Research, university staff and students, and exploration company geologists. All geological map data are held in a geographic information system, are available in digital form, and as thematic maps at various scales. The accompanying illustrated text summarises the regional geology and tectonic development, the economic and engineering geology, and the potential geological hazards.

The Raukumara Range is formed ofTorlesse composite terrane indurated sandstone and mudstone, of Late Jurassic to Early Cretaceous age. In western Raukumara Peninsula Torlesse basement is unconformably overlain by an Early Cretaceous cover sequence, but in the east the nature of the contact is still disputed. Late Cretaceous to Oligocene sandstone, mudstone and minor limestone were deposited in a passive margin setting. The boundary between the Australian and Pacific plates propagated through the region in Early Miocene time with emplacementofa series ofthrust sheets (the East CoastAllochthon) and deposition ofthick Miocene to Pliocene clastic sequences.

Rapid uplift and changes in sea level during the Quaternary have resulted in extensive alluvial terraces, floodplain deposits and uplifted marine terraces. Erosion and landsliding are widespread. Seismicity levels are typical for an area at the Australian-Pacific plate boundary, and further damaging earthquakes can be expected in the future. Oil and gas seeps are common and the first commercial discovery ofhydrocarbons was made near Wairoa in 1998.

The shore platform at Auroa Point, Mahia (y19/388232), exposes gently dipping, Late Miocene tuffaceous sandstones of the Tolaga Group, interpreted as turbidite deposits from a deep marine environment. The beds are cut by an orthogonal joint pattern.

Photo CN42J72: D.L. Homer

ISBN 0-478-09708-5