50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

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sharp when viewed remotely, which has led to speculation over its role as an active structure. On the other hand, it may be a relic of past tectonism, perhaps reactivated as a border fault early in the history of rifting within the TVZ, but no longer the focus of extensional strain. Recent fieldwork has better delimited the outcrop areas of some TVZ ignimbrites so that they can be used as chronostratigraphic marker horizons to determine the extent of Quaternary movement on the Hauhungaroa block. Offset of the Ongatiti ignimbrite (1.2 Ma) together with a lack of offset on the younger Whakamaru group ignimbrites (0.32 Ma) constrain the last Hauhungaroa Fault movement to 0.32-1.2 Ma. In the southern sector of the range, NW-trending minor faults offset the Ongatiti ignimbrite to expose the peneplaned greywacke surface of the range top. These structures align with steps in the gravity profile of the western boundary of the TVZ and their origin may be related to reactivation of preexisting basement faults. Faults further to the east have been covered by the voluminous Whakamaru Group ignimbrites obscuring any direct observation of pre-0.32 Ma faults. NE trending lineaments are observed east of the Hauhungaroa Fault, suggesting that faulting youngs to the east. We infer that the Hauhungaroa Fault block is an early structural feature within the TVZ and the locus of extensional strain has migrated to the east during the last 300 k.y. In addition to addressing the question of tectonic activity on the Hauhungaroa block, detailed field mapping in the south east of the range has revealed the presence of a new heavily eroded andesite cone in the area previously mapped as the Hauhungaroa Lahars. The eastern portion of this cone appears to by cut by a NE-trending fault that defines in part the western shore of Lake Taupo. Re-examination of the Hauhungaroa Lahar type locality (T18/435634) leads us to suggest that this locality is a lava flow with pronounced spheroidal weathering. However, detailed mapping shows that both lava flows and laharic material are present, along with colluvial material. The latter has locally mantled the underlying Tertiary sediments (Otunui Formation), acting as an armour and locally preserving the pre-Pleistocene peneplaned surfaces. POSTER SPATIAL AND TEMPORAL SEDIMENTATION PATTERNS SUGGEST RAPID, MARGIN-WIDE MUD DISPERSAL AT POVERTY BAY, NEW ZEALAND Alan R. Orpin 1 , Clark Alexander 2 ,J.P.Walsh 3 , Steve Kuehl 4 &LionelCarter 1 1 NIWA, Private Bag 14-901, Kilbirnie, Wellington, New Zealand 2 Skidaway Institute of Oceanography, Savannah, GA 31411, USA 3 Department of Geology and Coastal Resources Management Program, East Carolina University, Greenville, North Carolina 27858, USA 4 Virginia Institute of Marine Science, College of William and Mary, Gloucester Pt., VA 23062, USA (a.orpin*niwa.co.nz) On the eastern Raukumara Ranges active tectonics, vigorous weather systems, and human colonisation have caused widespread erosion of the mudstoneand sandstone-dominated hinterland. The Waipaoa River sedimentary dispersal system has responded to such changes, and is now New Zealand’s second largest river in terms of suspended sediment discharge. New sediment accumulation rate data for the Poverty Bay continental shelf and slope derived from radiochemical tracers ( 234 Th, 7 Be, 210 Pb, 137 C), palynological, tephrostratigraphic, and seismic methods suggest rapid, margin-wide dispersal of Waipaoa sediment. A post-glacial mud lobe on the outermost shelf and uppermost slope has been a locus of high sedimentation rates, attaining 40 m thickness in a structurally controlled sub-basin. Here, an offset in the last-glacial erosion surface indicates that deposition was sympathetic with fault activity and the creation of accommodation space, implying that sediment accumulation was not supply limited. Contrary to classical shelf sedimentation models, the highest modern accumulation rates of 1 cm/y occur in three depocenters: one on the outermost shelf, and two on the mid-shelf landward of shelf-edge anticlinal ridges. Shelf rates are about 10 times more than the mid-slope plateau. Moreover, short-lived 7 Be activities indicate fluvial sediment is rapidly reaching the outer shelf and upper slope. Similarly, at sub-millennial time scales, pollen records from slope cores fingerprint Polynesian followed by European settlement, and broaden the spatial extent of post-settlement sedimentation initially documented from the Poverty shelf. Changes in sedimentation infer a 2-3 times increase in accumulation on the shelf after European settlement, but a smaller 1-2 times increase on the slope. Over longer time scales, seismic evidence infers slower but steady sedimentation since the last transgression, and that significant cross-shelf sediment pathways pre-date the increase in sedimentation resulting from colonisation and deforestation. ORAL 50 th Kaikoura05 -64- Kaikoura 2005
THE GRIFFENS ROAD TEPHRAS: VALUABLE MARKER BEDS IN MAPPING THE QUATERNARY OF THE MANAWATU- WANGANUI REGION A. Palmer 1 ,J.Begg 2 ,D.Townsend 2 & K. Wilson 3 1 Soil and Earth Sciences, INR, Massey University, PB 11-222, Palmerston North. 2 Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt. 3 Research School of Earth Sciences, Victoria University, PO Box 600, Wellington. (a.s.palmer*massey.ac.nz) The age of many of the terraces, their cover beds, and underlying units in the lower Manawatu- Wanganui region, has until recently been poorly known. West of Wanganui, the map of Pillans (1990) provides a detailed temporal and spatial record of marine terraces and their cover beds. In Rangitikei, the aggradation terraces on the western side of the river have been mapped by Milne (1973), with minor revisions made by later authors. There remained large tracts of poorly known uplifted terrace land, some folded into growing anticlines. Theses by Massey University and Victoria University students provided some insight into the age and distribution of some of the mid-late Pleistocene deposits. However, recent examination of the landscape during Q-mapping have provided a timely rationale for re-evaluation and integration of the stratigraphic record. Critical to determining the age of the landscape, has been the recognition and identification of the Griffens Road tephras, the Fordell Ash, and the Rangitawa Pumice. The ca. 350ka Rangitawa Pumice (aka Mt Curl Tephra) was already well known on the Aldworth river terrace that formed in Marine Oxygen Isotope Stage (MOI) 10, the Ararata marine terraces (MOI 11) and older terraces. The Griffens Road Tephras, a group of three rhyolitic beds (informally “upper”, “middle” and “lower”), were previously known from sites north of Marton (Pillans 1988), and a few sites between the Whanganui and Turakina Rivers (Woolfe 1987, Bussell and Pillans 1992). The slightly younger Fordell Ash, was also found near Wanganui. The Griffens Road tephras are found in the marine sands, dune sands, gravels and loess that form the Galpin, Marton, Halcombe-Mt Stewart and Feilding anticlines and southern and western flanks of the Pohangina anticline, allowing surfaces in the area to be mapped with confidence. All three may be found in loess on river terraces that can now be correlated to the MOI 10 Aldworth terrace. The middle and upper tephras occur in the marine and terrestrial deposits of the MOI 9c (Braemore) marine terrace. Neither the Griffens Road tephras, nor the slightly younger Fordell ash are found on the wave-cut surface of the MOI 9a (Brunswick) marine terrace, suggesting that they all were deposited between 340 and 300ka. Tentative correlations are made to ignimbrites in the Central North Island. Bussell, M., Pillans, B., 1992. Vegetational and climatic history during oxygen isotope stage 9, Wanganui district, New Zealand, and correlation of the Fordell Ash. Journal of the Royal Society of New Zealand, 22: 41-60. Pillans, B., 1988. Loess chronology in Wanganui basin, New Zealand. In: Eden,D.N.andFurkert,R.J.(eds), Loess, its Distribution, Geology and Soils, pp175-191. Balkema, Rotterdam. Pillans, B., 1990. Late Quaternary marine terraces, south Taranaki-Wanganui (sheet Q22 and part sheets Q20, Q21, R21 and R22), 1:100,000. New Zealand Geological Survey Miscellaneous Series Map 18. Woolfe, K.J., 1987. The geology of the Turakina- Whangaehu interfluve. Unpublished B.Sc. (Hons) thesis, Victoria University. AUTOSUSPENSION: THEORY AND EXPERIMENT POSTER H.M. Pantin School of Earth & Environment, University of Leeds, Leeds LS2 9JT, UK (pantin*earth.leeds.ac.uk) An autosuspension current may be defined as a particle-driven gravity flow (turbidity current), which can persist indefinitely without any external supply of energy. Such a current is capable of entraining additional sediment, leading to acceleration. The critical combination of velocity, sediment content, and turbulent energy needed for the current to persist is known as the ignition point (Parker et al., 1986). In their analysis, Parker et al. (loc. cit.) restricted their investigation to spatiallydeveloping currents, and to those in the supercritical field (densiometric Richardson number Ri < 1). The Parker et al. model can appropriately be used on those submarine channels where topography, sediments, or bedforms provide evidence of active autosuspension. A good example is the Kaikoura Canyon � Hikurangi Channel system, east of New Zealand (Lewis & Pantin, 2002). When the model was applied to this channel system, with plausible values of bottom slope, flow thickness, and sediment grade, it was found that autosuspension was indeed possible, under suitable conditions. However, it was also found that whenever an ignition point was obtainable, the Ri number always fell within the supercritical field. The suspicion grew that perhaps, in the subcritical field 50 th Kaikoura05 -65- Kaikoura 2005
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CHARACTERISATION OF NEW ZEALAND NEP
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myrtaceous. One 20 mm diameter flow
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ange of lower resolution or fragmen
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CRETACEOUS-EOCENE TRANSGRESSION MAR
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consists of a well-developed canyon
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model. The relative position of the
Page 13 and 14: converts to plate theory. Thus, the
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Page 17 and 18: the LGM grass peak. This period of
Page 19 and 20: offshore west coast to offshore eas
Page 21 and 22: 4 Institut de Recherche pour le Dé
Page 23 and 24: VEGETATION AND CLIMATE CHANGE AT TH
Page 25 and 26: wider range. The youngest layer has
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Page 29 and 30: TRACKING CRUSTAL DIFFERENTIATION AN
Page 31 and 32: EMPIRICAL SCALING RELATIONS FOR SEI
Page 33 and 34: hydrovolcanic eruptions then took p
Page 35 and 36: and that the MTL marks a Late Carbo
Page 37 and 38: faunal changes within these cores w
Page 39 and 40: material at subsurface depths of se
Page 41 and 42: survived through in low numbers in
Page 43 and 44: in the TVZ and southern Havre Troug
Page 45 and 46: Tephra beds are commonly used to ai
Page 47 and 48: The MCC is bounded by deep-seated t
Page 49 and 50: distal alluvial plains where large
Page 51 and 52: Many of the molluscs in the highly
Page 53 and 54: incremental slip history and paleoe
Page 55 and 56: This paper explores what we know of
Page 57 and 58: volcanism and a linear vent oriente
Page 59 and 60: These areas are also described in
Page 61 and 62: 3D IMAGING OF THE FORE- AND BACKTHR
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Page 69 and 70: with 63.8%, and then [3] with 49.9%
Page 71 and 72: U-Th-Ra disequilibria data. In part
Page 73 and 74: landslide tsunami in the past. Rece
Page 75 and 76: core complex mode, temperature driv
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Page 85 and 86: The new era of commercial viability
Page 87 and 88: TECTONICS OF THE GALATEA BASIN USIN
Page 89 and 90: performed by the electron backscatt
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Page 93 and 94: Most of the tectonic blocks in the
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