New Zealand Journal of abstracts
Reconnaissance sediment and microfossil analyses of
a
laminated short piston core from Lake
Tekapo, South
Island, New Zealand
D. C. Mildenhall
U. A. Cochran
R. A. Cook
GNS Science
PO Box
30368
Lower Hutt 5040, New
Zealand
Abstract A 2.2 m piston core from the main
basin of Lake Tekapo
comprises
millimetre–centimetre-scale alternations of light and dark laminae. Two
much
thicker layers occur near the base of the core and are interpreted as
major
slump deposits. Light laminae are predominantly fine silts with low
microfossil
concentrations. Dark laminae have higher clay, mica, and microfossil
content
and higher planktic/benthic diatom ratios. These findings are
consistent with
light laminae being deposited during times of high river flow and high
sediment
input, the thickness and number forming a proxy for paleoclimate
(rainfall,
water inflow, and erosion rates), and the dark laminae being deposited
by
settling out of the water column during periods of low inflow. The
distribution
of pollen from plants introduced to New
Zealand
by Europeans, and the inconsistency of dominant pollen types between
samples,
suggests that the entire sequence is only c. 100 yr old and that
couplets of
light and dark laminae form more frequently than annually. With
appropriate
processing, diatoms, spores, and pollen are present in great enough
numbers in
the dark laminae to be used for paleoclimate reconstruction. Diatoms
are
predominantly planktic lacustrine forms with some benthic forms sourced
from
the lake margins. Pollen and spores are derived from local grasslands,
montane forest, fell fields, and tussock lands, and from West Coast
lowland
forest. Palynomorphs are carried over the central Southern
Alps
by prevailing northwesterly winds, and are deposited in the lake. The
presence
of fresh-looking Casuarina and possibly Banksia and Eucalyptus
pollen shows that it is likely that some pollen came from Australia.
It is believed that the presence and abundance of West Coast derived
pollen,
particularly Dacrydium cupressinum, and to a lesser extent Ascarina
lucida, Nothofagus, and Podocarpus/Prumnopitys
species, could be used as a proxy for the intensity and persistence of
northwesterly winds.
Keywords New Zealand; Lake
Tekapo;
palynology; pollen
dispersal; pollen deposition; Pinus; diatoms; wind direction;
laminae;
sedimentation; Recent
:
463–476
0028–8306/06/4904–0463 © The Royal Society
of New Zealand
2006
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