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The Influence of Glacial-Interglacial Climatic Transitions on Coarse-Grained Braided River Deposits

A. Rowan*, M. Jones, S. H. Brocklehurst, and S. Covey-Crump
School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK
*Corresponding author; Email: [email protected]; Telephone: +44(0)161 306 9360; Fax: +44(0)161 306 9361

Sediment supply to fluvial systems is controlled by a number of processes that occur at a basin-wide scale in the landscape and at a variety of time scales, which are in turn controlled by climate, geology and tectonics. The causes and effects of changes in both total sediment volume and grain size distribution supplied to braided river systems are considered, using examples from eastern South Island, New Zealand. These large gravel braided rivers have built up the Canterbury Plains to 600 m+ thick, and there is excellent coastal exposure over at least 70 km perpendicular to flow direction. These fluvial sediments are considered to represent a period of at least 30 ka that includes the New Zealand LGM, making them an excellent record of changes in fluvial processes and their deposits across a major climatic event. The field area has relatively uniform bedrock geology, and the dominant structural trend is the northeast-southwest trending Alpine fault, which causes consistency in tectonic controls and climate on either side of the range, along with a major across-range asymmetry in uplift rates and orographic precipitation. The fluvial stratigraphy has been surveyed to create high-resolution 2D stratigraphic panels to examine differences in fluvial architectures both across the floodplain and through time, consider how much of the transported sediment accumulates in the systems, and the processes from which these deposits result. OSL dating is used to determine absolute ages and so link key surfaces to the considerable climate record for New Zealand and the Southern Hemisphere.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid