New Zealand Journal of Geology and Geophysics abstracts
Glacial geology of the Cobb valley, northwest Nelson
JAMES SHULMEISTER
ROBERT MCKAY
CHRISTIANE SINGER
WILLIAM MCLEA
School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
Abstract Investigations of the Cobb valley in northwest
Nelson, New Zealand, yield evidence of at least two and possibly as many as
four phases of glaciation in the valley and adjacent areas. (1) The oldest of
these advances is undated, but is probably mid Quaternary, as it is preserved
on old valley floor remnants c. 100 m above the modern valley. Before the next
recorded glacial advance, periglacial conditions occurred at least briefly in
the valley. (2) The valley was then overrun by a glacier that deposited two
basal tills and probably extended into the modern fluvial gorge. The extensive
roche moutonnée fields through much of the valley and the basal tills
near the Cobb Dam may relate to this advance. (3) The moraine underlying the
Cobb Dam is inferred to be an end moraine of Last Glacial Maximum age (LGM). A
suite of recessional moraines extends upvalley from the head of the Cobb
Reservoir. The second of these has a minimum age of 17 000 radiocarbon
years and is consistent with an LGM interpretation for the Cobb Dam moraine. It
is possible that the LGM and deglacial sequence outlined in (3) is the retreat
phase of advance (2). (4) Deglaciation was rapid, but there is circumstantial
evidence for a temporary readvance from some cirques during the deglaciation.
There are no known Holocene glacial deposits.
Keywords glacial geology; Quaternary; northwest Nelson;
moraine
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44: 47-54
0028-8306/01/4401-0047 $7.00/0 (c) The Royal Society of New Zealand
2001
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