A study is being made of late Quaternary sediments of the Canterbury Plains and offshore Canterbury Bight region of the South Island. The aim of the work is to investigate the interplay between fluvial sediments deposited by large braided rivers, and their transition into marine deposits in the offshore region. This area offers a depositional continuum from a tectonically rising mountain chain to the west, across a broad braidplain, to a marine shelf and slope setting to the east.
The region is characterised by high rates of hinterland uplift and sediment delivery to the adjacent subsiding sedimentary basins that have experienced relatively minor deformation. It offers an opportunity to examine the response of a classical fluvial-marine transition to Late Quaternary Milankovitch-scale, glacio-eustatic sea-level fluctuations. This fluvial-marine transition has changed from lowstand shoreline positions 125 m below present-day sea-level, to highstand positions near to the present coastline throughout the Quaternary.
Stratigraphic architectures have been determined from high-resolution
3.5 kHz seismic reflection profiles and indicate a complex interplay of
braidplain advances during periods of sea-level fall punctuated by periods
of erosion and stranded coastal deposits during transgressions. Seven
unconformity-bound depositional sequences are recognised, and these are
thought to represent deposition through the last 700 ka.
Key findings to date
Keywords
Forced regressive deposits, sequence stratigraphy, Canterbury Plains,
Canterbury Bight, gravel bed rivers, shelf deposition, braided rivers.
References
Browne, G.H. 2001. Gravel size characteristics in braided rivers of
the mid-Canterbury Plains, New Zealand. Abstract. International Association
of Sedimentologists International Conference on Fluvial Sedimentology,
Lincoln, Nebraska, August 2001.
Browne, G.H.; Naish, T.R. 2001. Quaternary depositional cyclicity in the
Canterbury Bight, New Zealand. Abstract. International Association
of Sedimentologists 21st Conference, Davos, Switzerland, 3-5 September
2001.
Browne, G.H. 2002. A large-scale flood
event in 1994 from the mid-Canterbury Plains, New Zealand, and implications
for ancient fluvial deposits. In: Flood and Megaflood Deposits ed.
P. Martini. Special Publication of the International Association of
Sedimentologists 32, 99-109.
Browne, G.H.; Naish. T.R. 2003. Facies
development and sequence architecture of a late Quaternary fluvial-marine
transition, Canterbury Plains and shelf, New Zealand: implications for
forced regressive deposits. Sedimentary Geology 158, 57-86.
Naish, T.R.; Browne, G.H. 2003. Response of a Late Quaternary fluvial-marine margin to the 100,000 year climate cycle, Canterbury Plains, New Zealand. Abstract. INQUA Quaternary Workshop, Westport, New Zealand, January 2003.
July 23, 2003