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Radiocarbon Chronology and Problems in Its Interpretation for Quaternary Loess Deposits—South Canterbury, New Zealand¹

ABSTRACT

The sequence of events for the loess deposits on the Timaru Downs as indicated by ¹⁴C dating of clay-organic complexes, and whole and fractionated peat deposits is as follows: present soil and surficial peat have been forming from present to 9,900 years BP; uppermost loess was deposited between 9,900 and 11,800 years BP; first palesol and buried peat was formed 11,800 to 31,000 or more years BP; and the second loess was deposited > 31,000 years BP.

The mean residence time (MRT) of clay-organic complexes from the B2 horizon of the modern soil and paleosols was compared to the MRT's of fractionated and unfractionated samples of organic material from stratigraphically related peat deposits. In this study the chronology from whole organic samples was improved by dating fulvic acid, humic acid, and residence (humin) fractions. Humic acid fractions gave consistently older dates than residue fractions. The relative amount of these three fractions provides information about subsequent contamination. Concentrated organic deposits are preferred. However, clay-organic complexes of paleosols can be used to approximate the chronology of events after a correction for age at time of burial if contamination by organic material through leaching during subsequent soil development can be accounted for. The clay-organic complex method may extend ¹⁴C dating to paleosol horizons enriched with clay (B2 horizons) but devoid of organic enriched horizons (peat, muck, or A horizons).

¹ Contribution from the Dep. of Soil Science, Lincoln College, Univ. of Canterbury, New Zealand, and the Dep. of Agronomy, Univ. of Illinois, Urbana. Supported in part by a Senior Post-Doctoral Fellowship to the senior author while on sabbatic leave from the Univ. of Illinois and by a research grant from the Univ. Grants Committee, New Zealand.

² Former Senior Post-Doctoral Fellow, Lincoln College and Prof. of Soils, Univ. of Illinois; Senior Lecturer, Lincoln College; and Director, The Institute of Nuclear Science, DSIR, Lower Hutt, New Zealand, respectively. The authors would like to acknowledge the assistance of Charles Moore, ¹⁴C Laboratory, The Institute of Nuclear Science; P. J. Tonkin, Lecturer, Lincoln College; and Margaret Gibbons, Technician, Lincoln College.

Received for publication December 18, 1972. Accepted for publication April 30, 1973.