Late Neogene stratigraphy of the Carrington area, western Wairarapa, North Island, New Zealand

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This article was downloaded by: [University of California Santa Cruz]On: 11 November 2014, At: 06:58Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UKJournal of the Royal Society of NewZealandPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tnzr20Late Neogene stratigraphy of theCarrington area, western Wairarapa,North Island, New ZealandPatricia E. Wells aa Research School of Earth Sciences , Victoria University ofWellington , New ZealandPublished online: 14 Feb 2012.To cite this article: Patricia E. Wells (1989) Late Neogene stratigraphy of the Carrington area,western Wairarapa, North Island, New Zealand, Journal of the Royal Society of New Zealand,19:3, 283-303, DOI: 10.1080/03036758.1989.10427183To link to this article: http://dx.doi.org/10.1080/03036758.1989.10427183PLEASE SCROLL DOWN FOR ARTICLETaylor & Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms& Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/loi/tnzr20http://www.tandfonline.com/action/showCitFormats?doi=10.1080/03036758.1989.10427183http://dx.doi.org/10.1080/03036758.1989.10427183http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions Journal of the Royal Society ofNew Zealand,Volume 19, Number 3,1989, pp 283-303Late Neogene stratigraphy of the Carrington area, westernWairarapa, North Island, New ZealandPatricia E. WelIs*Nearly two kilometres of mostly marine sediment accumulated in western Wairarapaduring Late Neogene basement subsidence, Fossil content and lithological trends withinthe Upper Neogene marine strata record episodes of rise and fall in sea level which arerelated to the combined effects of basement subsidence, local faulting and tilting andglobal changes in sea level. The stratigraphy of western Wairarapa is similar to thatdescribed for Upper Neogene sediments adjacent to the Aorangi Range in south-eastWairarapa. The oldest Cenozoic sediments exposed in the Carrington area, west ofCarterton are a fining-upward sequence of fluvial then marine conglomerate, sandstone,siltstone and deep water, tuffaceous mudstone (Mangaoranga Formation of Neef,1974), which accumulated during rise in sea level between lOMy BP and 5.5 My BP. Fallin sea level after 5.5 My BP is indicated by a sudden change in lithology to shallowwater limestone (Hururua Limestone Formation; new name). The limestone containswell rounded and polished cobbles of Torlesse greywacke which were derived fromareas of uplift nearby. Massive mudstone and turbidite (Mangatarere MudstoneFormation; new name) accumulated during the Early Pliocene. The top of the formationconsists of bioturbated mudstone and very fine sandstones which have been reworkedby shallow and turbulent seas at the end of the Early Pliocene epoch (Opoitian Stage),coinciding with the sudden fall in global sea level after 3.2 My (Haq et al., 1987).A hardground breccia accumulated above an early Middle Pliocene (Waipipian)unconformity and forms the base of the Tea Creek Limestone (new name) member ofthe Carrington Formation (new name).This is conformably overlain by a massive,fossiliferous siltstone of Middle-Late Pliocene age (Waipipian to Mangapanian Stage),(Boys Siltstone, new name) which is the youngest marine sediment exposed in westernWairarapa. The Carrington area is structurally complex and is cut by several splinterfaults of the Wairarapa Fault Zone. The Upper Neogene strata are poorly exposed andare covered in places by middle Pleistocene (Te Muna Formation) conglomerates andmudstone which accumulated during regional uplift and emergence after 2My BP, and aset of upper Pleistocene river aggradation gravels.Key Words: New Pliocene stratigraphic units, Hururua Limestone Formation, Mangatarere Mudstone Formation,Carrington Formation, Tea Creek Limestone member, Boys Siltstone member, Mangaoranga Formation, OnokeGroup, Soren Group, basementsubsidence, Miocene-Pliocene boundary unconformity, middle Pliocene unconformity,hardground breccia, paleoecology, Upper Miocene conglomerate sedimentology, NZMS 260 S26, Wairarapa FaultINTRODUCTIONA sequence of Upper Neogene strata is exposed in the Carrington area, west of Cartertonin west Wairarapa, between the Tararua Ranges and the Wairarapa Plain (Fig. 1). Strata ofsimilar age are widely distributed throughout northwestern Wairarapa. This paper provides* Research School of Earth Sciences, Victoria University of Wellington.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014284 Journal of the Royal Society ofNew Zealand, Volume 19, 1989new stratigraphic information and paleoenvironmental interpretation, which enables correlationwith previously published stratigraphies of southeastern and northwestern Wairarapa andinterpretation of the timing and influence of local tectonics and global sea level fluctuationson Late Neogene sedimentation.The area has not been mapped in detail previously. It was described by Crawford (1870),and has been shown on geological maps by Ongley (1935), Kingma (1967) and Vella(1963a,b). Upper Pleistocene sediments of the northern part of the area were described byVella (1963a,b). The Mt Bruce area and the Eketahuna district to the north were mapped byWells (1987) and Neef (1974, 1984) respectively. To the east, the Mauriceville district wasmapped by Orbell (1962) and Holdgate (1972).Upper Neogene strata in the Carrington area are distributed in three broad belts which aresubparallel to (but not completely delineated by) a set of splinter faults of the Wairarapa Fault(Fig. 2). The exposed Tertiary strata are grouped into the Mangaoranga Formation of theSoren Group (Upper Miocene) and the Hururua Limestone, Mangatarere Mudstone andCarrington Formations of the Onoke Group (Pliocene).Throughout the text six-digit grid references are used to indicate the location of sampleswithin the Carrington area (part of NZMS 260 Sheet S26). Fossil localities within sheet S26are recorded in the New Zealand Fossil Record Files and are distinguished by their FossilRecord Number (f59 etc.).UPPER MIOCENE STRATIGRAPHYSoren Group (Neef, 1974), Late Miocene, Taranaki SeriesThe Soren Group comprises the Mangaoranga and Kaiparoro Formations in the Eketahunadistrict (Neef, 1974). Only the Mangaoranga Formation (Tongaporutuan to Kapitean) isexposed in the Carrington area.1o 20 40 Km~,,>'7J. :5.~ rEketahuna !~~ :" Mt BruceMikimiki '". __ Kopuaranga .. . . Matahiwi .Kaltuna.. ". _ TlrohanqaStudy area~ .... MastertonC' ,. I ~ 41Sarr~~gton , Carterton.' ..... ,.' 5.'7J.,,?'7J.04'~~'b-,...~~5.~ ~,.Q '7J.~~175E 176 EFig. 1 - Southern North Island. New Zealand, showing study area and other locations mentioned in thetext. Dotted line represents State Highway Two.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 285At the type section along Mangaoranga Stream in the Eketahuna District, the MangaorangaFormation consists of a 660m thick, fining-upward sequence of conglomerate, marl, sandstone,siltstone and mudstone of Tongaporutuan age.In the Carrington area a fining-upward, conglomerate to mudstone sequence with anage range of Tongaporutuan to Kapitean is assigned to the Mangaoranga Formation. Thesequence is exposed in a broad band in the west of the mapped area between the Te Hau,Wairarapa and Carrington Faults (Fig. 2). It is estimated to be c. I,200m thick and is inferredto overlie Mesozoic greywake basement rocks (Tararua Formation of Neef,1974) whichoutcrop half a kilometre south of the southernmost exposure of conglomerate and sandstoneat the lowest exposed part of the Mangaoranga Formation (smi conglomerate, Neef, 1974).The top of the sequence is not exposed, but an unconformity is inferred between the massivemudstones at the top of the sequence and the pebbly, shallow water limestones of theoverlying Hururua Limestone Formation. No stratigraphic breaks were observed, and thesequence is considered to represent a single cycle of sedimentation during basement subsidenceand associated sea level fluctuations.The Mangaoranga Formation in the Carrington area, consists of conglomerate, sandstone,siltstone and mudstone members (sml conglomerate, sm3 sandstone, sm4 siltstone and sm5mudstone of Neef, 1974, respectively). A basal lignite-bearing member (smO mudstone)described as stratigraphically underlying the Upper Miocene conglomerates inthe Mt Brucearea (Wells, 1987) is not exposed here but local residents report that coal was removed fromnear the southern-most exposure of the formation at the beginning of the century (P. Ryan,pers. comm., 1986).A Tongaporutuan to late Kapitean age is assigned to the Mangaoranga Formation on thebasis of the age of the stratigraphically overlying sediments at Carrington, Mt Bruce andEketahuna (Wells, 1987; Neef, 1984).Conglomerate member (sm1 conglomerate; Neef, 1974).In the Carrington area a sequence of alternating sandy conglomerate and sandstone isdistributed over c. one square kilometre to the north of Hoeke Road, northwest of Carterton(Fig. 2). The unit is considered to be biostratigraphically similar to the conglomerate of theMangaoranga Formation (sml conglomerate of Neef, 1974) in the Eketahuna district and isa correlative of the lower to middle Tongaporutuan conglomerates northwest of the AorangiRange of southeastern Wairarapa (Sunnyside Conglomerate; Vella and Briggs, 1971). Theconglomerate is estimated to be over 500m thick (Fig. 3) although only the top 250m are wellexposed. It is typically metre-bedded, clast-supported, moderately to well-sorted, with asandy matrix and weak iron oxide cement; composed almost entirely of greywacke clasts,and alternating with massive, yellow-brown, moderately- to well sorted sandstone.Sets of pebbles in six conglomerate horizons in the top 250m of the conglomerate weremeasured for shape (form and sphericity), roundness and imbrication (Table lA),The dominant pebble forms were bladed, compact bladed and compact elongate (FigA)which are the characteristic forms of river pebbles (Sneed and Folk, 1958). The sphericity ofthe pebbles at the top of the conglomerate unit ranges about the boundary of that characteristicof fluvial and beach environments whereas the sphericity of stratigraphically lower pebblehorizons are typical of fluvial environments. Clast roundness is well developed at allhorizons, with values ranging between 0.6 and 0.72 on the roundness scale of Krumbein(1941). Such well-developed roundness suggests deposition some distance from source,precluding a source in the greywacke of the immediately adjacent Tararua Ranges.Measurement of pebble imbrication at six horizons in the top 250m of the conglomerate(Table lA and Fig. 5) indicate paleocurrent flow initially from the east then from thenorthwest and northeast. The overall fabric of the conglomerate indicates a northeasterlysource of the conglomerates, precluding a source from the Aorangi Range to the southeast(Fig.1).Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014286 Journal of the Royal Society ofNew Zealand, Volume 19,1989Me sozo icPlioce neL.' . Mloc e ne~~1-'b~... ....1-u. o~.f\.ANorthw t South st cFB\ W F. . ._ OmG1 ~- .'Cn7f'ATHF-2 0 0~ , ,-1 0 0 '; I . . . . . . , .j~~.~. -:~:::-. -,...--,;--..,.....--- Om 'C 1 :n:- ?THFFig. 2A-C - Geological maps and cross sections. Maps based on NZMS 270 Sheet S26. Fig.2A showsthe geology of the southern part of Carrington area, with the geological legend showing the symbolsused to represent the main stratigraphic units, discussed in the text and shown in Fig. 2B (map ofnorthern part of study area). In Fig. 2B, symbol I = dip and strike; 2 =known bedding contact; 3 =inferred bedding contact; 4 =unconfonnity; 5 = known fault; 6 = inferred fault; 7 = thrust fault; 8 =airphoto lineament; 9 = Anticline axis; 10 = Syncline axis; 11 = terrace edge; 12 = fossil locationdiscussed in text; 13 = outcrop. Triangles = trigonometrical points; black squares = houses. Thelocations of Porewan, Ratan and Waiohine aggradation gravel surfaces are after Grapes and Wellman(1988). In Fig. 2C, THF = Te Hau Fault; CF = Carrington Fault; W(M)F = Mauriceville Fault or 1855trace of the Wairarapa Fault, and AF = Alfredton Fault.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 287~ 2 __ 3 ..- - 4~IJ5~ -d7~ 8 __ --8k1 0J(' IV 12& 1 3 XB\,:I~ ,.,,-,."Te HauuThe conglomerate unit is overlain by marine sandstone (fossil sample f27), so it is possiblethat at least the top part has been reworked and redeposited during the marine transgressionover the underlying alluvial gravels. Metre- to decimetre bedded conglomerate and sandstonenear the top of the conglomerate have uniform bed thickness and lateral persistence that istypical of wave-dominated gravels (Clifton, 1973). Samples of fine sandstone from near thetop of the unit were examined for fossil content, but all samples (e.g. f26) were found to bebarren; this does not preclude a marine origin since diagenesis and weathering commonlyresult in leaching of fossils from such permeable sediments.The environment of deposition of the conglomerate is inferred to have been initiallyfluvial, deposited by rivers flowing from the east and north, with subsequent reworking of thetop of the member during marine transgression.Thirteen kilometres to the north-north-west of Hoeke Road, along Black Creek Road nearKaituna, well-rounded, clast-supported, greywacke conglomerates overlie an eroded greywackebasement surface. These conglomerates were measured for roundness, shape and fabric, toenable comparison with the Carrington (Hoeke Road) conglomerates (Table IB).The Mikimiki gravels are very similar in shape to those at Hoeke Road (Fig.4), withdistribution over the same form classes and sphericity values > 0.66, indicating fluvialdeposition, similar to all but the top of the Hoeke Road gravels. The roundness of theMikimiki conglomerates is bimodal: the boulders immediately overlying the eroded MikimikiSurface are less rounded than the stratigraphically higher cobbles and pebbles. Clast imbricationindicates a paleoflow from the northeast (Table IB) which generally agrees with the paleoflowof the Carrington conglomerates.The gravels along Black Creek Road have previously been included in the MikimikiFormation by VelIa (l963a) who inferred them to be Nukumaruan in age on the basis of veryweak paleontological evidence. Good paleontological dating of the Black Creek Roadsediments has not yet been established, but I propose that they are Late Miocene in age, onthe basis of their stratigraphic and structural relationship to Upper Miocene strata that I haveDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014288 Journal of the Royal Society ofNew Zealand, Volume 19, 1989mapped (Wells, unpublished work in progress) in the Matahiwi area further east (Fig.1). Theconglomerates exposed along Black Creek Road are on the upthrown (western) side of the TeHau Fault (Vella, 1963b) and I interpret that they also underlie the sequence of UpperMiocene mudstones to sandstones exposed to the east (on the downthrown side) of the fault.Sandstone member (sm3 sandstone, Neef, 1974).Conglomerate at Hoeke Road, Carrington, fines upward into sandstone which is massive,pale yellow-brown to grey, coarse and pebbly at its base, and fines upward into siltstone. Thesandstone is similar to the sm3 sandstone of the Mangaoranga Formation (Neef, 1974) inlithology and age as well as in its stratigraphic relationship to surrounding units.In the Carrington area, the sandstone outcrops between the Te Hau and Wairarapa Faultsin a kilometre-wide band adjacent to Hoeke Road, and a half-kilometre wide strip adjacentand parallel to Hururua Road (Fig.2). Macrofossils at the latter location (f27 and f32) have anage range of Altonian to Tongaporutuanand include the molluscs Cucullaea sp.cf. hamptoni,Struthiolaria (Callusaria) callosa. (Sl-Tt) and Tropicolpus milleri (Pl-Tt) which, togetherwith the presence of the Tongaporutuan foraminifera Notorotalia pristina (in sample f27),indicate a Tongaporutuan age for the sandstone. The sandstone is interpreted to haveaccumulated in shallow water as it contains the typically shallow water foraminiferidNonionellina flemingi. The Mangaoranga Formation sandstone of the Carrington area islithologically very similar to pebbly sandstone along the Ruamahanga River in the Mt Brucearea (Wells, 1987) as well as the Mikimiki Formation sandstone (Vella,1963a) near BlackCreek Road in the Kaituna area. In the latter location, a yellow-brown massive sandstone,containing thin layers of well-rounded and highly polished, greywacke lag gravels similar tothose observed at Carrington, overlies conglomerates above a tilted Mesozoic greywackebasement surface (pre-Mikimiki Surface of Vella, 1963a). Rare molluscan moulds andbarnacle plates indicate marine deposition for part of the sandstone at Black Creek, but thereare too few faunal remains to define an age with any certainty (cf Vella, 1963a). I considerthe Mikimiki Formation to be a correlative of the sandstone member of the MangaorangaFormation (sm3 sandstone, Neef, 1974).Siltstone and mudstone members (sm4 siltstone and sm5 mudstone, Neef, 1974).In the Carrington area the Mangaoranga Formation sandstone is conformably overlain byand fines upward into siltstone then mudstone which are lithologically similar to siltstonesand mudstones of the Mangaoranga Formation (sm4 siltstone and sm5 mudstone, Neef,1974) at Mt Bruce (Wells,1987) and Eketahuna (Neef, 1974). In the Carrington area, thesiltstone-mudstone sequence is estimated to be 300m thick (Fig. 3) and is sporadicallyexposed from Enaki Stream (near Hoeke Road) to northwest of Tea Creek Road (Fig.2);further northwards it is covered by Pleistocene alluvium but are exposed again furthernorthwest, near Matahiwi, northwest of Masterton.In the Carrington area the siltstone is massive, blue-grey, and tuffaceous and grades upinto massive, blue-grey, fossiliferous mudstone. Sample f33 (at S26/207247) containsGloborotalia miozea conoidea and G. conomiozea, indicating a Kapitean age. The presenceof species of the Karreriella Biofacies (Vella, 1962) within the sample, together with ashallow water assemblage of microfossils, indicate deposition at a depth of c. 300m, with theshallow water fauna mixed in by down-shelf transport. Massive blue-grey mudstone at S26/235273 (sample f42) near Tea Creek Road contains the foraminifera Cibicides ihungia andGloborotalia conomiozea, indicating an early Kapitean age of deposition. The presence ofKarreriella cylindrica and absence of shallow water microfauna indicate a paleobathymetryof c. 300m.Neef (1984) reported two thin ash beds in the mudstone of the Mangaoranga Formation inthe Eketahuna district. Two Upper Miocene rhyolitic tuffs are exposed within the MangaorangaDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 289Quaternary gravels: Fluvial conglomerate and sandstone.- - - - Te Muna Formation: Metre-bedded, clast-supported~greywacke conglomerates alternating with massivemudstone. Porewan, Ratan and Waiohine aggradation. II~ gravels.Unconformity I Siltstone Over 200m. Massive, blue-grey; contammg:r oJr::rr.9'- ';;~ Semicrassus marwicki, Coluzea spectabilis, Penionhaweraensis and Pelicaria clarki. Coarsens up into sandy- II siltstone.Limestone 3-7m, Metre-bedded, brown pebbly limeIHardground breccia and bored concretions in sandyII .1 ':'::; ,IJo..o0 '1 ' "~ I :. c : -; ~ N_. . ..... c ...-. :: 0Q.. .. ; c u '"~. 1 ' 1-,~ .u ..c 0 - ..'" 0 ...c .. 0 1'00_cI~..0.. cc I ... - N 1-- .- ..Ic I,~0 I .'! : : I ... 0 .. _ .. 0 0 ... IILimestone c. 80m. Massive, brown, mollusc-rich, sandy,pebbly'Iime grainstone (calcarenite) with well roundedand polished greywacke cobbles. Contains abundantPhialopecten ongleyi and Mesopeplum convexum.Inferred unconformity. Contact faulted in places.Siltstone c. 100m. Massive, blue-grey .Fines up toSandstone c. 300m. Massive, yellow-brown. Coarse atbase, with common lag deposits of well rounded andpolished greywacke pebbles. Very fossiliferous; containsCucullaeacf hamptoni,Struthiolaria (Callusaria)callosa.Regional unconformity above greywacke basement.Fines up toGrades up toConglomerate alternating with massive sandstone. c.500m. Poorly sorted, clast-supported greywackeconglomerate. Unfossiliferous.Mudstone c. 250m. Massive, blue-grey. Fossiliferous;contains foraminifera Globorotalia miozea conoidea, G.conomiozea and Cibicides ihungia. Tuff bed near top.. .- u \27 ~~:.................., --X~~~(~k.::.~.~o-.: ~00. 0 0 0-::~'~:)"';\~:~ -o o.o8~cf' 0 ' . .....'~ ;; "oo.o . :~!,! -...... s ..:00:: "ao~ti,J.go :0;," ~Y.. : ~ :~0 9~"g:ibcoOO".0.u: "0 :.0' 0 ' " . a .o'? o '!.Q11E,& ..~/.00_Euco .. c ; Ic....,c c ..-.. ..o ~- 0a ...- c 0....Fig. 3 - Composite stratigraphic column for the Carrington area. N.Z. Fossil Record Numbers (f numbers)are shown in their approximate stratigraphic positions to the right of the column. Basement rock isTorlesse greywacke of Mesozoic age. The patterns used to denote different stratigraphic units are the sameas in Fig. 2.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014290 Journal of the Royal Society ofNew Zealand, Volume 19, 1989Formation mudstone near Hoeke Road, Carrington. One is exposed to the west of the 1855trace of the Wairarapa Fault, at S26/193232 on the northern banks of an unnamed stream,700m due north of its confluence with the Enaki Stream. This tuff is c.30cm thick andoverlies siliceous mudstone which contain a radiolarian fauna (sample f40) with speciesindicating a Tongaporutuan age (G.Ashby, pers.comm., 1986). The other tuff bed is creamywhite and at least 3m thick, and is exposed in a 100m long ridge adjacent, subparallel to andeast of the Wairarapa Fault, where it is cut by the Enaki Stream at S26/194216. The overlyingmudstone contains a sandy horizon fifteen metres above the tuff: this horizon has gradedbedding and burrow orientations indicating that the strata are overturned. Foraminifera fromthe mudstone stratigraphically overlying the tuff bed (f44) include Globorotalia conomiozeawhich indicates a Kapitean age.Environment ofdeposition ofMangaoranga FormationThe sedimentology of the lower part of the Mangaoranga Formation conglomerate in theCarrington area shows that deposition of the formation started in a fluvial environment.Fossil evidence indicates that the sandstone above the conglomerate was deposited inshallow seas which deepened to c. 300m by the end of the Miocene Epoch, when themudstone member was deposited.The fining-upward trend in the lithology of the formationCompact.9.8.7.6.3.2.1I K X X'" J( J( ')( x J( > Elongated.4 .5L-VL-SFig. 4 - Sphericity-Form diagram for particle shapes (after Sneed and Folk, 1958). L, I and S: long,intermediate and short diameter ofclasts. Verbal form classes C, P, Band E: Compact, Platy, Bladed andElongated. Carrington conglomerates shown by black squares, Kaituna-Mikimiki conglomerate shownby smaller, half-filled squares. Sample plots all cluster about the Compact Bladed - Compact Elongate- Bladed classes, indicating a fluvial origin.PlatyDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 291Table 1 - A: Pebble morphology and fabric data for Upper Miocene (Tongaporutuan)conglomerates sampled at Hoeke Road west of Carterton. B: Upper Miocene conglomerateoverlying pre-Mikimiki Surface (Vella, 1963) in the Kaituna-Mikimiki area.A: HoekeRoadwestof CartertonPosition Locationabove Grid* Roundness Fonn Sphericity Fabric Samplebasem't (n) SjL L-IjL-S M** (n) Number(metres) x sd x sd x sd x sd630 186215 (34) .69 .10 .56 .12 .71 .15 .77 .08 032,052(41) 7540 179216 (30) .65 .08 .46 .10 .52 .26 .66 .10 006 (73) 6540 179216 (36) .65 .12 .43 .12 .50 .24 .63 .13 006 (73)520 180215 (36) .61 .07 .51 .12 .55 .24 .63 .17 336,006 (100)5440 183215 (30) .72 .09 .50 .14 .65 .24 .71 .09 061 (54) 4430 181214 (36) .68 .12 .43 .12 .50 .24 .63 .13 3420 181214 (31) .65 .07 .48 .12 .52 .25 .68 .10 331,010(30) 2410 182214 - 067,087(73) 1B: Mikimiki-Kaituna area.50 246330(29) .68 .11 .58 .10 .73 .17 .78 .0720 243326(16) .70 .10 ..53 .11 .64 .18 .74 .0920 243326(31) .70 .11 .56 .12 .63 .21 .76 .10 035(74)10 252330(28) .50 .09 .56 .14 .47 .31 .72 .1210 252330(24) .50 .09 .49 .18 .47 .22 .67 .13_* Grid reference to NZMS 260 Sheet S26. (n) = numberof measurements. x = mean. sd = standarddeviation.** bearingin degreesfrom magnetic north(add 23 degreesfor bearingfrom true north).also suggests that deposition took place in a progressively deepening sea. Where theMangaoranga Formation has been examined elsewhere in Wairarapa (Neef, 1984, Eketahuna;Wells, 1987, Mt Bruce) a similar trend of deposition in progressively deepening seas duringthe Late Miocene has been inferred.In the Carrington area the oldest marine sands are of Tongaporutuan age indicating thatmarine conditions were established over the area between 10-5 My BP. Although the exacttiming of the transgression is not well constrained by field evidence I consider that it wascaused by the combined effect of the gradual rise in global sea levels throughout the LateMiocene (Vella, 1968; Haq et al., 1987; Fig.9) and the onset of basement subsidencethroughout western Wairarapa from the beginning of Late Miocene time (Wells, in prep.).PLIOCENE STRATIGRAPHYIn south-east Wairarapa, the Onoke Group (Vella and Briggs, 1971) is a sequence ofUpper Miocene limestone and Pliocene greensand and limestone unconformably overlyingbasement greywacke and a correlative sequence of mudstone and limestone unconformablyoverlying Upper Miocene mudstone and conglomerate in southeast Wairarapa. In theCarrington area the sequence of Lower Pliocene limestone and mudstone and Upper Pliocenelimestone and siltstone is assigned to the Onoke Group because of their lithological andbiostratigraphic similarity to mudstone and limestones of that group in southeast Wairarapa(Vella and Briggs, 1971).In the Carrington area the Onoke Group consists of shallow water limestone, deep watermudstone, turbidites and bioturbated mudstone to fine sandstone: it is divided into thefollowing formations and members (informal members in parenthesis):Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014292 Journal of the Royal Society ofNew Zealand, Volume 19,1989Formation Member AgeCarrington Boys SiltstoneTea Creek LimestoneMangatarere Mudstone (Mudstone, turbidite, sandstone)Hururua LimestoneWaipipian - MangapanianWaipipianOpoitianEarly OpoitianHururua Limestone Formation (new name), Lower Pliocene: Early OpoitianThe type locality of the Hururua Limestone is a disused limestone quarry, 300m southeastof Hururua Road (after which the formation is named) at S26/ 211237, on a farm trackleading to the crest of Carterton Bush Hill. The limestone is brecciated for c. 20m east of the1855 trace of the Wairarapa Fault. East of the fault zone it is a massive, sandy to granular,poorly sorted fossiliferous calcarenite (mollusc-rich grainstone) with very well rounded andpolished greywacke pebbles and cobbles and abundant mollusc macrofossils.The formationis not well exposed and is estimated to be c. 80m thick.The lower boundary of the limestone is not exposed at the type locality or elsewhere, butc , Ill.,D" ..I_'e' " .r .,I n.n I ... 0... ~E?Fig.5 - Pebble imbrication plots for six samples of Upper Miocene conglomerate from MangaorangaFormation (Tt-Tk) at Hoeke Road, Carrington, west of Carterton. Dip and dip direction (bearing frommagnetic north) taken from the ab plane of clasts, plotted on a Schmidt Net, contoured with a squared gridand corrected for tilt: arrowed B shows effect of rotation on bedding; thickened arrows shows effect ofrotation on areas of maximum concentration. n = number of clasts measured in each sample. Samplenumbers correspond with data in Table 1. All bearings from magnetic north (add 23 degrees to convertto bearing from true north). The six plots indicate paleocurrent flow from a direction between east andnorth-northwest.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 293the presence of well rounded and polished cobbles of greywacke in the limestone suggestthere were areas of exposed basement rock nearby. An erosional contact with thestratigraphically lower mudstones is inferred, and is supported by the presence of anunconformity at the Miocene-Pliocene boundary in the seismic profile through the area(Cape et al., unpublished). The top of the formation grades upward through sandy marls intomassive mudstone of the Mangatarere Mudstone Formation.Limestone at the type locality (sample f47) contains the mollusc Mesopeplum convexum(Tt-R) and the lower Pliocene (Opoitian) index fossil Chlamys (Phialopecten) ongleyi. As itis stratigraphically overlain by mudstone of early Opoitian age (lower part of MahgatarereMudstone Formation) and is itself inferred to overlie Mangaoranga Formation mudstone ofKapitean age, the age range for the limestone is restricted to the base of the Early Pliocene(early Opoitian).At the type section the limestone is exposed in a narrow belt c. 200m long and less than80m wide and appears to thin rapidly to the north and south, probably due to truncation at anoblique angle by the Wairarapa Fault. The Hururua Limestone is not exposed elsewhere inwestern Wairarapa.There are no Opoitian limestones reported from the Eketahuna, Mauriceville andKopuaranga districts (Neef 1974,1984; Orbell, 1962; Holdgate, 1974); in Hawke's Bay, theKairakau Limestone (Harmsen,1985) contains Phialopecten sp. indicating an Opoitian agebut it has been assigned to the late Opoitian by Harmsen (1985). The lower HaurangiLimestone (Vella and Briggs, 1971), exposed at the northern side of Aorangi Range insoutheast Wairarapa containing Phialopecten ongleyi and considered to be Opoitian in age, ishere regarded as a correlative of the Hururua Limestone.The presence of shallow water molluscan fossils and very smooth and well roundedgreywacke cobbles (maximum diameter of 30cm) in the sandy limestone suggests that it wasdeposited in shallow water (tens of metres), with the greywacke clasts derived from nearbytopographic highs and smoothed and rounded by nearshore wave-action. The lower HaurangiLimestone is also a shallow water facies which developed above a submarine anticline(proto-Aorangi Range) at the beginning of the Opoitian. Similarly, conglomeratic limestoneof Opoitian age in the Hawke's Bay district developed on marine planed surfaces of greywackeat the northern end of the Ruahine Ranges are interpreted to have been barnacle banks formedin shallow water near local areas of eroding greywacke basement (Beu et al.,1980).The development of an unconformity above Kapitean Stage sediments in the Carringtonarea before the deposition of early Pliocene limestone may be due to the combined effect ofglobal fall in sea level at this time (Haq et al., 1987; Fig.9) and local uplift associated witheither fault movement or tilting associated with folding.Mangatarere Mudstone Formation (new name), Lower Pliocene: OpoitianThe type section for the Mangatarere Mudstone Formation is in Mangatarere Stream,100m eastward from the 1855 trace of the Wairarapa Fault to 100m east of the bridge on TeaCreek Road, Carrington (S26/225254 to S26/230252; Figs 2B, 3 and 6). There, the followingsequence is exposed:(Top) (Carrington Formation)Massive (bioturbated) silty fine sandstone 4mCovered interval 95mMassive blue grey mudstone 17mAlternating sequence of graded fine sandstone and mudstone 1.39mCovered interval 67mMassive blue grey mudstone (occasional sandstone beds near top) 113m(Base) (1855 trace of the Wairarapa Fault)Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014294 Journal ofthe Royal Society ofNew Zealand. Volume 19. 1989At the type section massive blue grey mudstone grades up into turbidite, consisting ofaltemating sandstone and mudstone units. The base of each sandstone unit is typically sharpwith medium sand fining upwards to very fine, silty sandstone before grading into mudstone.In the middle part of the type section the units are typically 30cm thick, but this thicknessprogressively diminishes upward until the turbidite grades into 100% mudstone. Wheresedimentary structures have not been disturbed by bioturbation, incipient load casts, flamestructures and convolute bedding can be seen in the thinner (finer grained) units, suggestinggenesis from turbidity currents. A covered interval obscures the nature of the change frommassive blue-grey mudstone (sample f56) to massive (bioturbated), silty, fine sandstone atthe top of the formation at the eastern end of the type section (a low bluff adjacent to theMangatarere Stream at S26/230253; Fig.7). North of the type section gritty, muddy sandstoneat the top of the formation is exposed in a small unnamed stream cut by the 1855 trace of theWairarapa Fault, east of Tea Creek Road, 2.4 km north of Mangatarere Valley Road, at S26/238268. Less than 10m of the sandstone is exposed here, and it is massive, well sorted, rustyyellow-brown to greenish-grey and medium to fine grained. Extensive bioturbation hasremoved almost all trace of the original laminate mudstone.The lower boundary of the formation is not exposed at the type section but is exposed atS26/203229 (c. 250m north of the bridge near the junction of Hinau Gully Rd and HururuaRoad, in a small unnamed stream flowing west). This is designated a reference locality forthe basal part of the Mangatarere Formation: here massive blue grey mudstone is exposed ingradational contact with the sandy marls of the underlying Hururua Limestone. The upperboundary of the Mangatarere Mudstone Formation is an angular unconformity, exposed atthe eastern end of the type section (in the low bluff adjacent to the Mangatarere Stream atS26/230253; Fig.7) and 1.4 km further north (immediately adjacent to and east of the 1855trace of the Wairarapa Fault, on the eastern bank of a small, unnamed stream, at S26/238268).Foraminifera in mudstone of the type section (sample f56, at S26/227251) include Cibicidesfinlayi, Lenticulina mamilligera, abundant Globorotalia puncticulata and some G. inflata,indicating an early Opoitian age. Mudstone east of Hururua Road (sample f48) containsMucronina multicostales, Sigmoilopsis zeaserus, Globorotalia sphericomiozea, G.erassaformis and G. puncticulata indicating an early Opoitian age. Mudstone exposed alongthe unnamed stream flowing south from the junction of Hinau Gully Road and Hururua Road(at S26/ 198222; f51) contains Cibicides finlayi, Globorotalia puncticulata, G. erassaformisand G. inflata indicating a middle Opoitian age. Sandstone exposed in a small unnamedstream truncated by the 1855 trace of the Wairarapa Fault, east of Tea Creek Road, 2.4 kmnorth of Mangatarere Valley Road, contains a diverse foraminiferal fauna (sample f57 at S26/237268) which includes Cibicides finlayi, Globorotalia puncticulata and Globorotalia inflata,indicating a middle to late Opoitian age. The formation thus spans the Opoitian Stage.DistributionThe Mangatarere Mudstone is distributed in a narrow belt c. 7 km long between theCarrington and Alfredton Faults (Fig. 2): it extends north under Quaternary gravels and isexposed again in the Matahiwi-Mikimiki area, northwest of Masterton.CorrelationMassive blue grey mudstone of Opoitian age is widespread throughout Wairarapa. Insoutheastern and eastern Wairarapa it has been assigned to the Mangaopari MudstoneFormation (Vella and Briggs, 1971; Crundwell, 1987). Massive blue grey mudstone ofOpoitian age is widespread in the Mauriceville district (Orbell, 1962), in the Kopuarangadistrict (northeast of Masterton; Cleland Creek Formation of Holdgate (1972, and in theEketahuna district (Eketahuna Mudstone of Neef, 1974). In central and southern Hawke'sDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 295Fig.6 A - Part of the type sectionof the Mangatarere MudstoneFormation; looking towards NNEfrom S26/228250. Distant hillsare Mesozoic greywacke (G),middle-distance hills are PorewanSurface gravels (P): the 1855traceof the Wairarapa Fault (W) islocated behind the pine trees onthe left.Fig. 6B - Enlargement of the left-hand part of the riverembankmentin Fig.6A, showing detail of theMangatarere Mudstone. Theturbidite facies of the formationis exposed here and consists ofalternating mudstone and fining-upward sandstone units which dip60 degrees to the east (right).Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014296 Journal of the Royal Society ofNew Zealand, Volume 19, 1989Bay, massive blue-grey mudstone (Mangatoro Formation; Harmsen, 1985) was deposited inthe central part of the Wanganui-Hawke's Bay seaway during the Opoitian Stage (Beu et al.,1980):Turbidites of Opoitian age are widely distributed throughout the Eketahuna and Kopuarangadistricts (Eketahuna Turbidite of Neef (1974,1984) and Cleland Creek Formation of Holdgate(1972), respectively). In the Kopuaranga district, Holdgate (1972) mapped the Ditton SandstoneMember of the Ardea Formation along a large distance at the equivalent stratigraphicposition to the top of the Mangatarere Mudstone Formation.Environment ofdepositionThe presence of the foraminifera Haeuslerella pliocenica, Karreriella cylindrica,Hoeglundina elegans, Cibicides finlayi and C. deliquatus in mudstones at the type section(sample f48) indicate deposition at a depth of c. 200m (Hayward, 1986). The sample alsoincludes a shallow water fauna with Dyocibicides biserialis and D. primitiva indicatingdownslope transport. The presence of Laticarinina pauperata, Notorotalia taranakia abundantplanktonic foraminifera and Karreriella spp. in sample f51 indicate deposition of the mudstoneon the upper part of the continental slope and the presence of abundant Karreriella cushmaniin sample f 56 indicaties deposition at depths of at least 300m (Vella, 1962) during early tomiddle Opoitian time. The sandstone member at the top of the formation (sample f57)contains Notorotalia zelandica and Zeaflorilus parri, indicating deposition in turbulentconditions at very shallow depth (Hayward, 1986), close to the upper Opoitian shoreline.The microfossil content of the Mangatarere Mudstone indicates that water depths of c.300m were established in parts of western Wairarapa during Early Pliocene time (OpoitianStage) and this phase of high sea level appears to coincide with high global sea levelsbetween 5.0-4.0My BP (Haq et al., 1987; Fig.9). The lowered sea level indicated by thereworked sandstone at the top of the formation appears to coincide with the postulated fall inglobal sea level near 3.8 My BP (Haq et al., op cit.), although local tectonics (e.g. upliftassociated with faulting or folding) may also have contributed to the apparent sea levelfluctuations.Carrington Formation (new name), Middle to Late PlioceneThe Carrington Formation is exposed northwest of Carterton in the Carrington area, afterwhich it is named. It consists of the Tea Creek Limestone and Boys Siltstone Members. Itstype locality is from 700 to 50m north of the Mangatarere Valley Road, along both banks ofthe Mangatarere Stream and in the small bluff 200m northeast of the bridge over theMangatarere Stream on Tea Creek Road (Figs 2B, 7 and 8).The formation is distributed west of the Mauriceville and Alfredton Faults from south ofCarterton Bush Hill to north of Boys Trig (Fig.2B): further east it is covered by Quaternarygravels of the Wairarapa Plain.Tea Creek Limestone Member (new name), Middle Pliocene: Waipipian.The Tea Creek Limestone is best exposed in low bluffs on the northern bank of theMangatarere Stream, east of Tea Creek Road (after which it is named) near Carrington,between S26/231254 and S26/230252, which is designated as the type locality. The limestoneis also exposed further north, east of the 1855 trace of the Wairarapa Fault and c. 150m eastof Tea Creek Road (S26/236266) which is designated as a reference locality. The memberranges in thickness from at least 7m at the type locality to less than 3m at the referencelocality.At the type locality (Fig.7) the base of the limestone is a hardground breccia, composed oflarge angular, tabular blocks of calcite-cemented, extensively bored, laminated mudstoneDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 297Fig. 7A - Type locality of the Tea Creek Limestone member of the Carrington Formation; view lookingsouth from 526/229254 towards Boys Trig. hill, showing the small bluff where Tea Creek Limestone (T)is best exposed. Large boulders of dislodged limestone (L) have collected at the base of the bluff. Theposition of the Middle Pliocene unconformity beneath the Waipipian limestone is indicated by the dashedline to the left; the smaller dashed line to the right indicates the inferred position of the Alfredton Fault.Fig. 7B - Closer view of the limestone (L), unconformity (dashed while line) and underlying sandstonefacies of the Mangatarere Mudstone (M). A fifty cent coin (diameter 30mm) is shown for scale. Largetabular boulders of brecciated hardground (B) overlie the angular unconformity at the base of the TeaCreek Limestone.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014298 Journal of the Royal Society ofNew Zealand, Volume J9, J989which are surrounded by coarse gritty sands containing abundant macrofossil fragments. Theoverlying limestone is a metre-bedded yellow-brown, poorly-cemented, brachiopod-richlime grainstone with common well rounded granules to small pebbles of greywacke. At thereference locality, a shelly conglomerate with bored mudstone concretions and granules andpebbles of greywacke, is present at the same horizon as the hardground breccia at the typelocality.The lower boundary of the limestone is an angular unconformity of c. 1.8 degrees, whichis exposed at the type locality. The limestone grades up into a massive brown medium-grained sandstone at the type locality (at S26/230253): this change has not been observedelsewhere but may represent the gradational upper boundary of the limestone member asBoys Siltstone is inferred to overlie the limestone eastwards from the reference locality (S26/236267) as far as the inferred position of the Alfredton Fault (Figs 2 and 7A).The limestone is very fossiliferous and sample f58 contains abundant Neothyris ovalis anda shallow water assemblage of molluscs which includes Chlamys gemmulata, Glycymerislaticostata, and Notocallista multistriata. The presence oflarge Pectens (including Phialopectentriphooki aff. marwicki, but not the usual Mangapanian subspecies: A. Beu, pers. comm.,1986) indicate a Waipipian (Middle Pliocene) age.The areas where the limestone outcrops are largely fault bounded. Less than a hundredmetres southeast of the type locality the massive limestone abruptly pinches out (by faulting)against massive siltstone of Late Pliocene (Waipipian to Mangapanian) age; the strata areupthrown to the west of the fault, which approximately aligns with the Alfredton Fault. Northof Mangatarere Stream the limestone terminates against the 1855 trace of the WairarapaFault.The Tea Creek Limestone is a correlative of the Awapapa Limestone (Waipipian Stage) ofthe Te Aute Group (Harmsen, 1985) of Central and Southern Hawke's Bay. In the Eketahunadistrict several Waipipian limestones are described as members of the Makuri SandstoneFormation (Neef, 1984). Limestone is found within Waipipian strata in the Mauricevilledistrict (Orbell, 1962). In the Kopuaranga district, Holdgate (1972) described pebbly calcariousgrits of Waipipian age at Tirohanga which may be a lateral facies equivalent to the Tea CreekLimestone. In southeast Wairarapa, the upper part of the Haurangi Limestone is inferred to beWaipipian in age (Vella and Briggs, 1971) and is probably also a correlative of the Tea CreekLimestone.Environment ofdepositionThe limestone initially was deposited on a brecciated hardground. Hardgrounds typicallyform during periods of submarine non-deposition and associated strong currents (c. Fleming,pers comm., 1987). The development of a horizon of bored mudstone concretions at anequivalent horizon further to the north indicates that while the hardground was developingnear the type section, current action winnowed away an unknown thickness of mudstone andconcentrated concretions further to the north (at the reference section). This phenomenon hasbeen described in Pliocene strata at Tauweru,c. 30 km to the east (McSweeny, 1987). Thecause of the brecciation of the hardground is not known. The brecciated hardground wasdeposited with coarse sands and granules of greywacke which were extensively burrowed byan active, shallow water marine biota which included abundant molluscs. A number of thefossil molluscs are species which are found today in shallow waters around New Zealand(Powell, 1979) including Notocallista multistriata, commonly found in fine sands at depthsof9m to 183m; Glycymeris laticostata, found in shallow water to c. 73m depth, living partlyburied in coarse sand and gravel; Chlamys gemmulata, found at shallow depths to 73m, andBaryspira mucronata, found in shallow water to depths of 45m. The presence of thesespecies indicates that the limestone accumulated at shallow depths, probably less than 50m.A phase of submarine erosion followed by clastic deposition was inferred for Waipipiansedimentation in the Hawke's Bay area by Beu et al. (1980), who associated such changesDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 299with the initiation of the East Coast inland depression.Before the deposition of the Middle Pliocene (Waipipian) limestone there was a period ofnon-deposition and erosion at the beginning of the Waipipian Stage. At this time a hardgroundsurface developed, while an unknown thickness of sediment was winnowed away fromconcretions within lower Waipipian sediment. These erosional/non-depositional eventscoincided with the large fall in sea level between 3.2My and 2.9 My BP (Hag et al (1987;Fig.9) and are consistent with a middle Pliocene (Middle Waipipian) age for the limestone.Boys Siltstone Member (new name), Middle-Late Pliocene: Waipipian toMangapanianThe type locality of Boys Siltstone is designated as the Mangatarere Stream near BoysTrig (after which it is named) from S26/230248 to S26/231245 (Fig. 8). There, massive,fossiliferous grey-blue siltstone to silty, very fine sandstone is exposed.The lower and upperboundaries of the member are not exposed, but the exposed part of the member is at least200m thick.Along the southwestern banks of the Mangatarere Stream (S26/228247) the siltstonecontains a diverse and abundant macrofauna (f59) which includes the Pliocene speciesMarama murdochi Marwick, Mesopeplum (Borehamia) crawfordi (Hutton), and Zeacuminiamurdochi Powell. A Middle Pliocene (Waipipian) or younger age is indicated by the presenceof the species Xenophora neozelanica Suter and Struthiolaria (Pelicaria) cestata Marwick,and a Waipipian age is indicated by the presence of the species Semicrassus (Kahua)marwicki (Fleming), Coluzea spectabilis Powell, Austrosassio pusulosa Marwick, Mauriahawera (Oliver), and Penion haweraensis (Powell). Early Mangapanian forms of StruthiolariaFig. 8 - Type section of the Boys Siltstone member of the Carrington Formation on the south bank ofMangatarere Stream, near S26/230246. View looking south from Tea Creek Rd towards MangatarereValley Rd. The middle-upper Pliocene, creamy-white siltstone (BS) is overlain by upper PleistoceneWaiohine Surface river aggradation gravels (W).Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014300 Journal of the Royal Society ofNew Zealand, Volume 19,1989(Pelicaria] clarki are present in samples f60 (S26/231246) and f63 (S26/233250). Associatedmicrofauna include Globorotalia inflata, G. puncticulata and dextrally coiled G. crassaformis,indicating a late Waipipian to early Mangapanian age (Hornibrook, 1982).The southernmost exposure of the siltstone is on a farm track across the southwestern edgeofCarterton Bush Hill, at S26/203219. The siltstone is distributed northward from there in abroad belt east of the Alfredton Fault northward to Mangatarere Stream, then between theMauriceville and Alfredton Faults northward along Tea Creek Road (Fig.2B).CorrelationThe siltstone may be a correlative of the Marima Sandstone (Neef,1984) in westernEketahuna and/or the Lower Makuri Siltstone of eastern Eketahuna, the latter of whichoverlies Waipipian siltstones near Mangamahoe, on the northern edge of the Mauricevilledistrict mapped by Orbell (1962). No siltstone of Waipipian age is known in Kopuarangadistrict (Holdgate, 1972). In southeast Wairarapa, Upper Mangaopari Mudstone and itsshallow water facies equivalent, Bull Creek Limestone (Vella and Briggs, 1971), are coevalwith the Tea Creek Siltstone.Environment ofdepositionThe siltstone contains a number of species of fossil molluscs which have livingrepresentatives in shallow waters around New Zealand today. These include the horse musselAtrina zelandica, today common on protected sand beaches, typically found on intertidalflats or below low tide level (Powell, 1979). Other subtidal species include the cockleNemocardium pulchellum, the otter shell Zenatia acinaces, the olive shell Baryspira mucronataand the sand-flat snail Struthiolaria papulosa. Specimens of the genus Alcithoe are present,which is found today on sandy beaches and mud flats (Powell, 1976): Zeacolpus vittatus,Poirieria zelandica and Zenatia acinaces are today commonly found around New Zealandfrom shallow water to depths of 180m (Powell, 1979). The mollusc Xenophora neozelanicais a deeper water species, found today at depths of 37-91m (Powell, 1976), and was probablyswept inshore during storms.QUATERNARY STRATIGRAPHYThe oldest middle Pleistocene strata exposed in the Carrington area is a sequence ofalternating conglomerate and pebbly, blue-grey mudstone, distributed over a broad area tothe east of the Wairarapa Fault from Hoeke Road in the south to Mangatarere Stream (Fig. 2).Lignites sampled from within the mudstone horizons near Hinau Gully Road (S26/l98218)were given amino acid racemization dates of c. 0.3 My (B. Pillans, pers. comm., 1986), whichis close to the younger age range of the Te Muna Formation at Huangarua in the southeastWairarapa (Collen and Vella, 1984).The Te Muna Formation is well exposed along the small unnamed stream flowing southfrom Hururua Road between S26/197221 and S26/199218). The conglomerate here is clast-supported with a sandy matrix and composed of well rounded greywacke clasts. The metre-bedded mudstone layers are commonly pebbly and carbonaceous. The conglomerates heredip 10-16 degrees to the southeast and are unconformably overlain by Upper Pleistoceneriver aggradation gravels; 100m further north, Te Muna Formation gravels have been foldedinto a near-vertical attitude by uplift along the Wairarapa Fault.The formation disconformably overlies massive blue-grey mudstones of the MangatarereMudstone Formation (Opoitian) at S26/203218. At S26/229243, an alternating conglomerate-mudstone sequence unconformably overlying Boys Siltstone (Carrington Formation;Waipipian) is inferred to be Te Muna Formation.Three river aggradation surfaces are well developed in the area and have been mapped asDownloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 301HoEdHaTwoL Tt wowo.... 'J:! co " 0' V1 .j>.0Age(MyBP)W IV .... 0-......Ae0..tit..'"... ..e ::Je'I t'l... 1;1;-e e.""Ctit.,-e...~e en0'eo.0"- ~....... ::Je I,Fig. 9 - Eustatic curves (from Haq et al., 1987). Geological time scales of Homibrook (1981), Edwards(1985) and Harmsen (1985) are shown coded as Ho, Ed and Ha. Tongaporutuan and Kapitean stages ofthe NZ Taranaki series (Late Miocene) are indicated by the symbols Tt and Tk; Opoitian, Waipipianand Mangapanian stage of the Wanganui Series (Pliocene) by the symbols Wo, Wp and Wm resp.Porewan, Ratan and Waiohine Surface gravels (c. 60, 30 and 11 thousand years oldrespectively), by Grapes and Wellman (1988).SUMMARY OF THE HISTORY OF LATE NEOGENE SEDIMENTATION INWESTERN WAIRARAPAThe fossil content and sedimentary character of the sequence of Upper Neogene strata inwestern Wairarapa record the following events:(1) Accumulation of a thick sequence of fluvial conglomerate and sandstone prior to earlyTongaporutuan marine transgression.(2) Accumulation of c. 1000m of marine sediment (Mangaoranga Formation) during theLate Miocene in progressively deepening seas, which reached a depth of c. 300m in lateTongaporutuan to Kapitean times.(3) Sudden shallowing at the end of Late Miocene time, probably the result of localfaulting and associated uplift/tilting, producing an unconformity.(4) Accumulation of shallow-water limestones (Hururua Limestone Formation) above theKapitean-Opoitian unconformity (probably a faulted or tilted, eroding submarine high)during the earliest Pliocene stage, followed by rapid deepening of the Pliocene seas to c.300m by early Opoitian time during which Mangatarere Mudstone Formation sedimentsaccumulated. Water depth was maintained at c. 300m until latest Opoitian time when the seasshallowed.(5) Submarine erosion and the development of an angular unconformity during the latestOpoitian and early Waipipian period, probably associated with local uplift and tilt as well asglobal fall in sea level; this was followed by(6) deposition of shallow water limestone (Tea Creek Limestone member of the CarringtonFormation) during Middle Pliocene (Waipipian) time, then shallow water SOm) siltstone(Boys Siltstone), in late Waipipian to early Mangapanian time.(7) Accumulation of fluvial sediments (Te Muna Formation) and younger gravels (Porewan,Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014302 Journal ofthe Royal Society ofNew Zealand, Volume 19, 1989Ratan and Waiohine surface aggredation gravels) over the Upper Miocene-Pliocene sequencefrom IMy ago.It is difficult to place specific dates on these events because (1) the chronology is based anfossil content, which are accurate only to within the 'early', 'middle' or 'late' division of aNZ Stage, and (2) there is lack of consensus as to the absolute time of the various NewZealand stage boundaries (compare the ages published by Hornibrook, 1981; Edwards, 1985and Harmsen, 1985 in Fig 9). Also, paleobathymetic accuracy is limited to the degree ofaccuracy of the present methods for determining the depth of Cenozoic sea (Vella, 1962;Hayward, 1986) and assessement of paleobathymetric trends is further limited by theincompleteness of the stratigraphic record. The paleobathymetric history of the mapped areawas influenced by a number of factors, including regional subsidence, local tectonism(faulting, folding) and global changes in sea level.Western Wairarapa underwent a phase of basement subsidence from the beginning of LateMiocene time until the end of Pliocene time, after which it began a phase of uplift andemergence which has continued through to present time. Superimposed on this generalsubsidence there have been a number of periods of basement faulting, folding and associatedtilting, which have at times enhanced the effect of global fluctuations in sea level (e.g.subsidence during periods of high sea level, as recorded during Late Miocene time whenMangaoranga Formation sediments accumulated in progressively deepening seas), while atother times the local and regional tectonics have completely masked the effect of global sealevel fluctuations (e.g. localised uplift at the end of Kapitean time resulted in the developmentof an unconformity above which shallow-water, pebbly limestones (Hururua Limestone)accumulated, even though this was a period of high global sea level (Fig.Sj).The Carrington area is structurally complex, and the Upper Neogene and Quaternary strataare cut by at least four faults, including the active transcurrent Wairarapa Fault. Myinterpretation of the structure and stratigraphy of the Carrington area suggests that theWairarapa Fault and associated splinter faults (Mauriceville, Carrington and Alfredton Faults(=Wairarapa Fault Zone; Fig. 2 did not have a significant effect on sedimentation until after2MYBP; before this time, the faulting and associated folding/tilting which controlledsedimentation and development of unconformities was located further east of the mappedarea. Where the Wairarapa Fault plane is exposed (S26/194217; north of Hoeke Road, on thesouth bank of Enaki Stream) it is a thrust fault, dipping 40 degrees to the west. This thrustingat shallow depths has resulted in the development of a recumbent fold in the Upper Miocenestrata adjacent (east of) the fault, and the Kapitean mudstones (and tuff beds) at S26/195215(f44) are overturned. Further north (at S26/197221, S26/203228 and S26/238269) upliftalong the 1855 trace of the Wairarapa Fault has tilted Upper Miocene to Quaternary sedimentsinto near vertical attitudes (c. 80 degrees). I interpret that the Wairarapa Fault itself is arelatively young feature of the geology of the area, and that horizontal movement along itbegan during the latest phase of a complex and multi-phased history in the development ofthe Wairarapa Fault Zone (work in progress).ACKNOWLEDGMENTSThe author is grateful to Associate-Professor P. Vella (Victoria University of Wellington)for discussion, help in fossil identification and editing several drafts of this manuscript;Dr P. Barrett (VUW) for helpful comments; Dr B. Pillans (VUW) for dating of severallignite samples by amino-acid racemization; Dr A. Beu (Geological Survey, DSIR) foridentification of macrofossils and Mr D. Cowe (Greytown) for supplying a faunal listfrom his own collection of macrofossils from Boys Siltstone. The manuscript hasbenefitted from the careful review and useful suggestions of an anonymous referee. Myresearch was supported by a University Grants Committee Postgraduate Scholarshipand the Internal Research Committee of Victoria University. I am also grateful forfacilities made available by the Geology Department of the Australian National Universitywhile I was a Visiting Fellow during 1987.Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014Wells - Carrington stratigraphy 303REFERENCESBeu, A.G., Grant-Taylor, T.L., and Hornibrook, N.de B., 1980. The Te Aute limestone facies, PovertyBay to northern Wairarapa. NZ. Geological Survey miscellaneous series map 13, 1: 25000 (2sheets) and map notes.Clifton, H.E., 1973. Pebble segregation and bed lenticularity in wave-worked versus alluvial gravel.Sedimentology 20: 173-187.Collen, J.D., and Vella, P., 1984. Hautotara, Te Muna and Ahiaruhe Formations, Middle to LatePleistocene, Wairarapa, New Zealand. 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Transactions of the RoyalSociety ofNZ., Geology 2 (2): 15-50.---1963b. Upper Pleistocene succession in the inland part of Wairarapa Valley, New Zealand.Transactions of the Royal Society ofN.Z., Geology 2(4): 63-78.---1968. Inferred temperature fluctuation at the beginning of the Taranaki Epoch (Upper Miocene).Tuatara 16 (I): 49-49.--.-and Briggs, W. M., 1971. Lithostratigraphic names, Upper Miocene to Lower Pleistocene,Northern Aorangi Range, Wairarapa. NZ. Journal ofGeology and Geophysics 14: 253-274.Wells, P.E., 1987. The stratigraphy and structure of the Mt Bruce area, northern Wairarapa, NorthIsland, New Zealand. Journal of the Royal Society ofNZ. 17(2): 101-113.Received 3 May 1988, accepted 27 October 1988Downloaded by [University of California Santa Cruz] at 06:58 11 November 2014

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