Luminescence chronology of loess‐paleosol sequences from Canterbury, South Island, 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 LI). At Barrys Bay an age of 70 ± 15 ka was obtained in the basal LI, and at Timaru two separate samples in the base of LI also yielded ages of c. 70 ka, thus correlating the entire Cust loess sequence with the LI 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-Ll 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.

Correlation of fluvial terraces within the Hikurangi Margin, New Zealand: implications for climate and baselevel controls

“…Although generally sparse, organic material is present as wood within the gravel-dominated deposits, and also occurs as peat in terrace cover deposits, and charcoal within tephras. Luminescence dating is being increasingly used in New Zealand to extend age control beyond the limits of radiocarbon dating, and has particularly been used to date loess (e.g., Berger et al, 1992Berger et al, , 2001Berger et al, , 2002Litchfield and Lian, 2004). The present study is the first to apply Optically Stimulated Luminescence (OSL) dating directly to fluvial deposits in the eastern North Island, although OSL ages of loess coverbeds have been used to estimate the minimum ages of river terrace deposits (Wang, 2001;Formento-Trigilio et al, 2003).…”

Subdividing the Pleistocene using the Matuyama–Brunhes boundary (MBB): an Australasian perspective

“…The older three layers are tentatively correlated with MOIS 10, 12 and 14 (or 16). Paleomagnetic results (Berger et al, 2001;Pillans, unpublished data) indicate normal polarity throughout. Thus, the entire loess column is assigned to the Brunhes Chron, despite the fact that it is directly underlain by 2.5 Ma basalt.…”

“…Six main loess units have been recognised (Runge et al, 1974), the youngest of which contains the 26 ka Kawakawa Tephra layer. Luminescence ages from the youngest three layers are somewhat problematic (Berger et al, 2001), but broadly indicate correlation with MOIS 2, 6, and 8. The older three layers are tentatively correlated with MOIS 10, 12 and 14 (or 16).…”

Luminescence age estimates of Pleistocene marine terrace and alluvial fan sediments associated with tectonic activity along coastal Otago, New Zealand

“…For the same reason mentioned above, this age must be considered a lower limit. However, if it is assumed that this loess formed during a glacial period, as is typical in the lower South Island (e.g., Berger et al 2001Berger et al , 2002, then sample WBE1 was probably deposited near the end of MIS 6 (186-128 ka), as it is unlikely that anomalous fading has resulted in an age underestimation of >300%, as would be the case if the sample was deposited during an older glaciation (i.e., during or before MIS 8). If this assumption is correct, then the overlying beach sand likely formed during the MISS 5e (128-113 ka) sea-level highstand.…”