New Zealand Journal of Geology and Geophysics abstracts
Luminescence chronology of loess-paleosol sequences from Canterbury, South
Island, New Zealand
GLENN W. BERGER
Desert Research Institute
2215 Raggio Parkway
Reno, NV 89512-1095, USA
email: gwberger@dri.edu
BRAD J. PILLANS
Research School of Earth Sciences
Australian National University
Canberra, ACT, 0200, Australia
PHILIP J. TONKIN
Division of Soil, Plant and Ecological Sciences
P.O. Box 84
Lincoln University
Canterbury, New Zealand
Abstract The extensive Quaternary loess-paleosol deposits of
South Island, New Zealand, represent one of the major proxy records of
paleoclimatic changes in the Southern Hemisphere. We attempted to produce the
first numeric chronology of these subaerial sequences in the Canterbury region
by using thermoluminescence and infrared-stimulated luminescence dating
methods. We examined five exposures: a 6 m thick section at Cust, north of
Christchurch; two thicker (c. 14 m) sequences on Banks Peninsula (Barrys
Bay and Onawe sites); farther south, a c. 12 m sequence in Timaru; and a c. 7 m
sequence on the coast at the Normanby site near Timaru. Our results are largely
based on single experiments per sample, and therefore provide imprecise ages
for several of the older samples. The most satisfactory results are those from
the youngest site (Cust), for which three samples were dated. Here, phases of
maximum loess deposition are dated at 73 +/- 13 ka (basal loess-paleosol unit
L3), 41 +/- 5 ka (basal L2), and 27 +/- 3 ka (basal L1). At Barrys Bay an age
of 70 +/- 15 ka was obtained in the basal L1, and at Timaru two separate
samples in the base of L1 also yielded ages of c. 70 ka, thus correlating the
entire Cust loess sequence with the L1 loess unit at these two other study
sites. Only at Barrys Bay were ages (c. 130-250 ka) in stratigraphic order
obtained for older samples (units L2 and deeper). At the other sites, some
samples in the sub-L1 units gave age reversals, and some (including the oldest
sample at Barrys Bay) yielded poor precision (e.g., 20%). Units L2 at Timaru
and Barrys Bay may correlate to all or part of MIS 6; however, the poor
precision and some age reversals in other units at these sites and at Normanby
and Onawe preclude any unambiguous correlations between sites or to the MIS
time-scale. Nevertheless, in the absence of any prior numeric ages, these first
results serve as a basis for more precise future dating of these units.
Although these reconnaissance dating results illustrate some of the problems
for luminescence dating of such sequences in South Island, they do provide a
beginning for a more accurate correlation of terrestrial and terrestrial-marine
sedimentary sequences in this part of the Southern Hemisphere.
Keywords luminescence; dating; geochronology; loess;
Canterbury; South Island
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
501-516
0024-8306/01/4404-0501 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (3090K); (scanned from paper original: notes about this process)
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