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, UK

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    Late 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: 10.1080/03036758.1989.10427183

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  • Journal of the Royal Society ofNew Zealand,Volume 19, Number 3,1989, pp 283-303

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

    Patricia 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 Fault

    INTRODUCTION

    A 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.

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  • 284 Journal of the Royal Society ofNew Zealand, Volume 19, 1989

    new 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 STRATIGRAPHY

    Soren Group (Neef, 1974), Late Miocene, Taranaki Series

    The 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.

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    Mikimiki '". __ Kopuaranga .. . . Matahiwi .

    Kaltuna.. ". _ TlrohanqaStudy area~ .... MastertonC

    ' ,. I ~ 41Sarr~~gton , Carterton

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    175E 176 EFig. 1 - Southern North Island. New Zealand, showing study area and other locations mentioned in thetext. Dotted line represents State Highway Two.

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  • Wells - Carrington stratigraphy 285

    At 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 Forma

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