Temporal and spatial complexity in post-glacial sedimentation on the tectonically active,Poverty Bay continental margin of New Zealand |
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| Institution: | 1. National Institute of Water and Atmospheric Research (NIWA), Private Bag 14-901 Kilbirnie, Wellington, New Zealand;2. Skidaway Institute of Oceanography, Savannah, GA 31411, USA;3. Virginia Institute of Marine Science, College of William and Mary, Gloucester Pt., VA 23062, USA;4. Department of Geology and Coastal Resources Management Program, East Carolina University, Greenville, NC 27858, USA;1. School of Oceanography, University of Washington, Box 357940, Seattle, WA 98195-7940 USA;2. Dept. of Geology and Geophysics, Boston College, Chestnut Hill, MA 02467 USA;3. U.S. Geological Survey, Coastal and Marine Geology, 384 Woods Hole Road, Woods Hole, MA 02543-1598 USA;1. Department of Geography, College of Science, Swansea University, Singleton Park, Swansea, Wales SA2 8PP, UK;2. Geography and Earth Sciences, Aberystwyth University, Llandinam Building, Penglais Campus, Aberystwyth, SY23 3DB Wales, UK;3. School of Geography and Geosciences, Irvine Building, St Andrews, KY16 9AL Scotland, UK;4. Scottish Association for Marine Science, Scottish Marine Institute, Oban PA37, 1QA, UK;5. School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK;6. Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, Copenhagen 2100 Ø, Denmark;7. Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland;8. Centre for Arctic Gas Hydrate, Environment and Climate (CAGE), Department of Geology, University of Tromsø, Tromsø, Norway;1. United States Geological Survey, 4210 University Dr., Anchorage, AK 99508, United States;2. Geological Sciences, California State University–Fullerton, 800 N. State College Boulevard, Fullerton CA 92834, United States;3. Department of Geosciences, Boise State University, 1910 University Dr., Boise, ID 83725, United States;4. United States Geological Survey, 12201 Sunrise Valley Drive, M.S. 905, Reston, VA 20192, United States;1. Department of Geography, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom;2. Department of Geography, Swansea University, Swansea SA2 8PP, United Kingdom;1. Sea Level Research Unit, Department of Geography, Durham University, Durham, DH1 3LE, UK;2. Geological Survey of Belgium, Royal Belgian Institute of Natural Sciences, Rue Jenner, Brussels, 1000, Belgium;1. Sea Level Research, Department of Marine and Coastal Science, Rutgers University, New Brunswick, NJ, USA;2. Asian School of the Environment, Nanyang Technological University, Singapore;3. Earth Observatory of Singapore, Nanyang Technological University, Singapore;4. Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile;5. Department of Geological Sciences, Central Washington University, Ellensburg, WA, USA;6. Geologic Hazards Science Center, U.S. Geological Survey, Golden, CO, USA;7. Division of Marine Science, School of Ocean Science and Technology, University of Southern Mississippi, Stennis Space Center, MS, USA;8. School of Mathematical Sciences, Insight Centre for Data Analytics, University College Dublin, Ireland;9. Department of Earth and Space Sciences, West Chester University, West Chester, PA, USA;1. Vancouver, V5L 2Z4, BC, Canada;2. Department of Earth Sciences, Simon Fraser University, Burnaby, V5A 1S6, BC, Canada |
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| Abstract: | On the eastern Raukumara Ranges of the New Zealand East Coast, active tectonics, vigorous weather systems, and human colonisation have combined to cause widespread erosion of the mudstone- and sandstone-dominated hinterland. The Waipaoa River sedimentary dispersal system is an example that has responded to environmental change, and is now New Zealand's second largest river in terms of suspended sediment discharge. This paper presents new sediment accumulation rates for the continental shelf and slope that span century to post-glacial time scales. These data are derived from radiochemical tracer, palynological, tephrostratigraphic, and seismic methods. We hypothesise on the temporal and spatial complexity of post-glacial sedimentation across the margin and identify the broad extent of sediment dispersal from the Waipaoa system. The ～15 km3 Poverty Bay mid-shelf basin lies adjacent to the mouth of the Waipaoa River, reaching a maximum thickness of ～45 m. A post-glacial mud lobe of an additional ～3 km3 extends through the Poverty Gap and out onto the uppermost slope, 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 sedimentation was not supply limited. Contrary to classical shelf sedimentation models, the highest modern accumulation rate of 1 cm y?1 occurs on the outer-shelf sediment lobe, approximately ～2 times the rate recorded at the mid-shelf basin depocentre, and ～10 times faster than the excess 210Pb rates estimated from the slope. Pollen records from slope cores fingerprint Polynesian then European settlement, and broaden the spatial extent of post-settlement sedimentation initially documented from the Poverty Bay mid-shelf. Changes in sub-millennial sedimentation infer a 2–3-times increase in post-settlement accumulation on the shelf 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. From a summation of coastal bedload, shelf and slope sediment mass accumulation, the total sediment budget for the Holocene is ～1 Mt y?1. Under modern conditions a larger proportion of the Waipaoa sediment dispersal system likely extends onto the slope and beyond. |
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