Radiometric Chronology

This paper provides a brief overview of the most common dating techniques applied in palaeoclimate and palaeoenvironmental studies including four radiometric and isotopic dating methods (radiocarbon, 230Th disequilibrium, luminescence, cosmogenic nuclides) and two incremental methods based on layer counting (ice layer, varves). For each method, concise background information about the fundamental principles and methodological approaches is provided. We concentrate on the time interval of focus for the INTIMATE (Integrating Ice core, MArine and TErrestrial records) community (60e8 ka). This dating guide addresses palaeoclimatologists who aim at interpretation of their often regional and local proxy time series in a wider spatial context and, therefore, have to rely on correlation with proxy records
obtained from different archives from various regions. For this reason, we especially emphasise scientific approaches for harmonising chronologies for sophisticated and robust proxy data integration. In this respect, up-to-date age modelling techniques are presented as well as tools for linking records by age equivalence including tephrochronology, cosmogenic 10Be and palaeomagnetic variations. Finally, to avoid inadequate documentation of chronologies and assure reliable correlation of proxy time series, this paper provides recommendations for minimum standards of uncertainty and age datum reporting.

Using a set of high-quality radiocarbon dates, including three new dates from the Hanson site and one from the Folsom component of Hell Gap, we provide a revised estimate of the duration of the Folsom period. Limiting our sample to bone collagen samples pretreated using the XAD resin chromatographic or ultrafiltration techniques, calcined bone, and charcoal from hearth features, we show that Folsom sites fall within a limited range from 12,610 to 12,170 BP, or 440 years. This duration is considerably shorter than previous estimates. Additionally, we show that there is little correlation between the onset and termination of the Younger Dryas and the start and end of the Folsom complex. Finally, the youngest Clovis sites and the last of the Pleistocene megafauna correlate well in time, but are followed by a 100-year gap until the earliest Folsom sites, most likely a result of small sample size.

The implicit purpose of the recent paper by Pike et al. (2012) appears to be to clarify or refine the chronology of the cave art of south-western Europe, most especially of the early phases of that sequence of traditions. The following is intended to show that the results they report will not necessarily rewrite that chronology any more than the efforts to refute the dating work at Chauvet Cave (Clottes et al. 1995, et passim) have succeeded in this. The reasons are as complex as a constructive discussion of the individual claims made, and their respective merits, but a small contribution to this will be attempted here.

Veronique Michel , Helene Valladas, Guanjun Shen, Wei Wang, Jian-xin Zhao,
Chuan-Chou Shen, Patricia Valensi, Christopher J. Bae
The origin of modern humans continues to be one of the most heavily debated topics within paleoanthropology. Eastern Asia, and particularly China, is a geographic region that is taking on increasing importance in resolving some of these debates...

This work presents a new age framework for the main Bashkirian glacio-eustatic transgression in Argentina, including the first absolute age for the Jejenes Formation, San Juan Province, based on radiometric dating of a crystal-rich tuff, supported by palynological and palaeofloristic studies, and presented within a revised palaeogeographic setting. The Jejenes Formation represents the glacial to postglacial fill of the Quebrada Grande palaeofjord carved in the Eastern Precordillera. The succession has been subdivided into five stages, the youngest of which suggests a previously unrecognised glacial event for this locality. Six productive levels for palynology were found within proglacial strata, and in the base and top of the succeeding interglacial stage. Palynoassemblages are characterized by poorly preserved trilete spores and monosaccate pollen grains along with a large amount of terrestrial phytoclasts. Main species indicating the Raistrickia densa-Convolutispora muriornata SubZone (DMa SZ) are Vallatisporites ciliaris, Cristatisporites rollerii, C. stellatus, C. chacoparanensis, C. inconstans and monosaccates such as Circumplicatipollis plicatus. This DMa SZ is estimated as Serpukhovian/Bashkirian and characterizes the glacial-related Guandacol Formation and equivalents units of the western Paganzo Basin. A tuffaceous level in the proglacial unit, bearing platyspermic seeds, plant remains and palynomorphs, yielded first-cycle volcanic zircons that were analysed by SHRIMP. An absolute age of 321.3 ± 5.3 Ma confirms a Bashkirian age for the main postglacial transgression in the Paganzo Basin, and offers a novel calibration for the palynoassemblages of DMa SZ that occurs elsewhere in Western Argentina.