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

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We have compiled the distribution of gas hydrates on the Fiordland margin based on the occurrence of BSRs in an extensive database of seismic reflection data, acquired by academic, government and petroleum research cruises over the last 30 years. Bottom simulating reflections (BSRs) are thereby found in an area of approximately 2200 sq km on the continental slope south-west. Main characteristics of the BSRs include: 1. predominately negative polarity compared to the seafloor reflection, which infers to a 2. decrease in acoustic impedance, the reflections follow the morphology of the seafloor, thereby crosscutting strata, and 3. strong variations of amplitudes with offset (AVO), indicating the presence of free gas below the reflection. In addition, the existence of free gas is supported by a reduced interval velocity distribution below the BSR, with velocity decreases of up to 30% compared to the overlaying layers. Because seismic reflection data is the only available data source in the Fiordland region (other a priori information like well information is not available) a simultaneous AVO inversion algorithm is used to obtain rock property attributes of P-impedance, vp/vs, and density, respectively. This information is used to verify the quantities of gas hydrate and their potential as a gas reserve in this region. POSTER MID-PLEISTOCENE EXTINCTION OF DEEP-SEA OSTRACODA? F.J. Gaiger &K.Swanson Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch (fjg17*student.canterbury.ac.nz) The last identified global marine extinction event (‘the Stilostomella extinction’) occurred about 600- 900ka during the mid Pleistocene climate transition. It is not only the most recent deep-sea extinction, but also least studied because recovery of sediments of that age and environment of deposition are still most effectively achieved by examination of relatively few, widely distributed cores. This extinction affected benthic foraminifera, in particular 82 species and 17 genera, including one complete family (Stilostomellidae – 21 species). A second family (Pleurostomellidae – 24 species) also suffered significant extinction, however two species of that group have been recovered in sediments which post-date the mid-Pleistocene event. In an attempt to determine whether benthic ostracods (Podocopida) have also been affected by the ‘Stilostomella event’ as an ongoing MSc thesis project, a single ODP core from the northern flank of the Chatham Rise, New Zealand, is being examined. Ostracods are crustaceans in which the soft anatomy is encapsulated in a bivalved, calcareous carapace. Valves of this microscopic organism are commonly preserved in deep-sea sediments and as result, ostracods present the most complete biogeographic and stratigraphic record of any metazoan in the deep sea. This fact provides an opportunity to examine whether more complex, benthic deep-sea marine organisms were also affected by the extinction event and if so, to then provide an additional insight into what environmental factors led to the significant loss of biodiversity. The results of this project will also make a contribution to our understanding of ostracod diversification through time with particular reference to significant Late Pliocene- Pleistocene events described for bradleyinid and trachyleberid species especially from the Southern Ocean. Significant problems relating to taxonomy and taphonomy have and continue to hinder progress. Samples studied are from the ODP core 1125 located about 600km east of the South Island at 1359 m depth on the northern side of the Chatham Rise. The samples are from the top of the core down to approximately 42 mbsf, covering the last 2.5 Ma, i.e. late Pliocene to Recent. There is a significant variation between samples in terms of grain size, ostracod population (total number of specimens and diversity) and the disproportionate number of juvenile valves. Some groups are well represented, including Bradleya, Taracythere, Krithe and Apatihowella, which form the main cluster of target species for this project. The occurrence of Bradleya pygmaea in core 1125 (1359 m) is significant because it has been recorded in Pliocene abyssal/bathyal sediments elsewhere in the Southwest Pacific, and was also recovered in uppermost Quaternary sediment from that Plateau. It is, however, no longer living on the Campbell Plateau, which implies steepening thermal gradients and an associated shoaling as significant influences on both the latitudinal and depth distribution of Podocopid ostracods. ORAL 50 th Kaikoura05 -28- Kaikoura 2005
TRACKING CRUSTAL DIFFERENTIATION AND ASSIMILATION PROCESSES AT ARC VOLCANOES: A URANIUM SERIES ISOTOPE PERSPECTIVE R. George 1 ,S.Turner 1 ,R.Price 2 ,C.Cook 2 &B. Finney 3 1 GEMOC Key Centre, Earth and Planetary Sciences, Macquarie University, Sydney 2 School of Science and Technology, University of Waikato, Private Bag 3105, Hamilton 3 Department of Earth Sciences, University of Bristol, Queens Rd, Bristol, BS8 1RJ, UK (rgeorge*els.mq.edu.au) Parent-daughter isotope systems that decay on time scales appropriate to the rates of processes themselves have proved powerful tools in tracking the histories of many arc-related processes from fluid release during plate subduction to dynamic melting of the mantle wedge. However, the rates inferred for mantle processes can only be considered real if the effects of continental crustal interaction are demonstrably minimal. In order to try and deconvolve mantle and crustal processes in this context we consider two contrasting case studies. Ruapehu volcano, New Zealand: On an equiline diagram the Ruapehu samples form a subtle positive array that extends from Taupo rhyolites and is intermediate between them and Kermadec lavas. It is conceivable from this data that a simple model of mixing between mantle-derived melts and Taupo crustal melts may explain the Ruapehu disequilibria. However, other reservoirs may be involved. For example, the range of calculated disequilibria derived from elemental Th/U ratios in averaged metasedimentary xenoliths, Torlesse and Waipapa basement averages could also be involved. Thus an alternative, although speculative, model is that Ruapehu samples reflect melts sourced from the lower to middle crust (as sampled in the xenolith suite), mixed with those generated at shallower levels (represented by Taupo-like magmas). Irrespective of the exact details of likely components, the key aspect of these systematics is that for the first time, there is sufficient information available to show that an inclined array on the equiline diagram for a single volcanic suite is unequivocally the product of open system processes: mixing between mantle or lower to midcrustal melts and shallow upper crustal components. Okmok volcano, Aleutian arc: At face value, 238 U- 230 Th disequilibria in young volcanics from Okmok suggest time scales of 50 kyr or less for some combination of mantle-crustal processes to take place. Given good evidence in the arc as a whole for fluid transfer from the subducted plate to take less than 10 kyr to reach the arc volcano (George et al., 2003), this additional time could reasonably be supposed to relate to a crustal process. Extremely good negative correlations between Sr and O isotopes are consistent with crustal assimilation of low � 18 O, hydrothermally-altered wallrocks. While the correlation between these two parameters and ( 230 Th/ 232 Th) appears to be less coherent, it is striking that these activity ratios broadly increase with increasing Sr isotope ratios and decreasing � 18 O. The assimilant could therefore be hydrothermally-altered arc crust of relatively recent age of less than 100 kyr. ORAL THE SURFACE IMAGE OF AN ACTIVELY GROWING – INVERTED? – REVERSE FAULT: THE OSTLER FAULT IN THE MACKENZIE BASIN (SOUTH ISLAND, NEW ZEALAND) F. C. Ghisetti Dept. of Geology, University of Otago, PO Box 56, Dunedin, New Zealand (francesca.ghisetti*stonebow.otago.ac.nz) A reappraisal of the geometry and structural evolution of the Ostler fault within the Mackenzie basin is under way. A new geological map of the fault zone (scale 1:50,000) is almost complete, and two seismic reflection lines across the fault will be acquired by A. Gorman in the early months of 2006 (Otago University Research Grant). The Ostler fault is a 50 km long, N-S reverse fault, dipping 30º-50º W. Previous studies have documented the segmented nature of the fault, average rates of deformation �1 mm/yr, and the occurrence of two seismic events in the last 6 ka. According to Kleffmann and Stern (in preparation) the Ostler fault bounds the edge of a strong gravimetric gradient of residual Bouguer anomalies, with a minimum < -200 µN/kg west of the fault. This setting is interpreted in terms of a buried marine Tertiary basin, controlled by earlier normal faults. The deep geometry of the fault is largely unresolved, but stratigraphic and structural features revealed by surface mapping need to be considered in any interpretation. A >1000 m thick sequence of terrestrial mudstones, siltstones and gravels (Pliocene?-Pleistocene?) is exposed in the fault hanging wall only. Internal architecture reveals a growth geometry of beds tilted 30º-60º W, unconformably overlain by coarse gravels (120 ka?). Above, six orders of river terraces are preserved, with the three highest orders correlating to the 35, 22-17 and 14 ka moraines. Terrace distribution indicates shifting of faulttransverse drainages, relatable to episodic uplift of the upthrown block during progressive northward propagation of segment ruptures in the late 50 th Kaikoura05 -29- Kaikoura 2005
Page 1 and 2: CHARACTERISATION OF NEW ZEALAND NEP
Page 3 and 4: myrtaceous. One 20 mm diameter flow
Page 5 and 6: ange of lower resolution or fragmen
Page 7 and 8: CRETACEOUS-EOCENE TRANSGRESSION MAR
Page 9 and 10: consists of a well-developed canyon
Page 11 and 12: model. The relative position of the
Page 13 and 14: converts to plate theory. Thus, the
Page 15 and 16: and on the following morning the mi
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
Page 27: few normal faults visible especiall
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
Page 63 and 64: ascending methane fluids/gases of p
Page 65 and 66: THE GRIFFENS ROAD TEPHRAS: VALUABLE
Page 67 and 68: sideritic concretions that occur in
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
Page 77 and 78: truncating three plutonic suites of
Page 79 and 80:
active, andesitic White Island volc
Page 81 and 82:
and voluminous than at any on Earth
Page 83 and 84:
oundaries and with immature source
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The new era of commercial viability
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TECTONICS OF THE GALATEA BASIN USIN
Page 89 and 90:
performed by the electron backscatt
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25km northeast of the volcano. Alth
Page 93 and 94:
Most of the tectonic blocks in the
Page 95 and 96:
TECTONIC AND NON-TECTONIC CAUSES OF
Page 97 and 98:
The continental shelf of the Povert
Page 99 and 100:
5 Dept. of Mineral Sciences, Smiths
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Adams CJ...........................
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Naish T............................
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