科研之友
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摘要
This paper combines the data sets available today for C-14-age calibration of the last 60 ka. By stepwise synchronization of paleoclimate signatures, each of these sets of C-14-ages is compared with the U/Th-dated Chinese Hulu Cave speleothem records, which shows global paleoclimate change in high temporal resolution. By this synchronization we have established an absolute-dated Greenland-Hulu chronological framework, against which global paleoclimate data can be referenced, extending the C-14-age calibration curve back to the limits of the radiocarbon method. Based on this new, U/Th-based Creenland(Hulu) chronology, we confirm that the radiocarbon timescale underestimates calendar ages by C-14 variations are several thousand years during most of Oxygen Isotope Stage 3. Major atmospheric observed for the period of the Middle to Upper Paleolithic transition, which has significant implications for dating the demise of the last Neandertals. The early part of "the transition" (with C-14 ages > 35.0 ka C-14 BP) coincides with the Laschamp geomagnetic excursion. This period is characterized by highlyelevated atmospheric C-14 levels. The following period ca. 35.0-32.5 ka C-14 BP shows a series of distinct large-scale C-14 age inversions and extended plateaus. In consequence, individual archaeological C-14 dates older than 35.0 ka C-14 BP can be age-calibrated with relatively high precision, while individual dates in the interval 35.0-32.5 ka C-14 BP are subject to large systematic age-'distortions,' and chronologies based on large data sets will show apparent age-overlaps of up to ca. 5,000 cal years. Nevertheless, the observed variations in past C-14 levels are not as extreme as previously proposed ("Middle to Upper Paleolithic dating anomaly"), and the new chronological framework leaves ample room for application of radiocarbon dating in the age-range 45.0-25.0 ka C-14 BP at high temporal resolution.
- 出版日期2008-11
