Abstract
ABSTRACTThe inland valleys of New Zealand’s South Island were heavily glaciated during the last glacial cycle. Subsequent fluvial incision has eroded out glacial deposits from the valleys in many locations, making it difficult to reconstruct glacial dynamics and chronology. The Brabazon and Butler Downs lie in a fault-controlled intra-montaine basin that has been largely protected from fluvial erosion and the area contains extensive evidence for multiple glacial margins. This paper presents a detailed glacial geomorphology map of the Brabazon and Butler Downs at a scale of 1:20,000. Glacial landforms have been mapped and subdivided into three main zones: an upper zone distinguished by a flight of kame terraces, a middle zone containing kettles and meltwater channels, and a lower zone of lateral moraines. The new map provides insight into former glacial environments in the region and provides a related framework for future paleoclimate reconstructions.
Highlights
The details of the geomorphological and sedimentary records in New Zealand provide high-quality evidence for investigating past climate fluctuations
Terrestrial cosmogenic radionuclide studies of moraine boulders have unlocked the chronology of the largest advances in the last glacial cycle (e.g. Schaefer et al, 2015; Shulmeister, Fink, Hyatt, Thackray, & Rother, 2010a), but advances of intermediate size are hard to reconstruct as the moraines are often destroyed by subsequent advances
Meltwater flowing around the sides of the glacier formed kame terraces; as the glacier stagnated, kettles formed; and at its smallest extent, recession moraines formed at the edge of the glacier
Summary
The details of the geomorphological and sedimentary records in New Zealand provide high-quality evidence for investigating past climate fluctuations. Fault-controlled intra-montane basins provide an unusual opportunity to investigate these intermediate-sized advances. These basins are areas where glacial flow diverges and glacial records, both sedimentary and geomorphological, may be preserved on the flanks of the basin. Many of these basins contain flights of kame terraces, other ice-marginal drainages, and lateral moraine sequences. The geomorphological map of the Brabazon and Butler Downs presented here supports ongoing sedimentary and geochronological investigations of this part of the Rangitata Valley in New Zealand, and is intended to enhance our understanding of glacial conditions during the last glaciation
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