Tephra isochrons and chronologies of colonisation

This paper demonstrates the use of tephrochronology in dating the earliest archaeological evidence for the settlement of Iceland. This island was one of the last places on Earth settled by people and there are conflicting ideas about the pace and scale of initial colonisation. Three tephra layers, the Landnám (‘land-taking’) tephra layer (A.D. 877 ± 1), the Eldgjá tephra (A.D. 939) and the recently dated V-Sv tephra (A.D. 938 ± 6) can be found at 58% of 253 securely-dated early settlement sites across the country. The presence of the tephras permits both a countrywide comparison, and a classification of these settlement sites into pre-Landnám, Landnám and post-Landnám. The data summarised here for the first time indicate that it will be possible to reconstruct the tempo and development of the colonisation process in decadal resolution by more systematically utilising the dating potential of tephrochronology

How 14 C dates on wood charcoal increase precision when dating colonization: The examples of Iceland and Polynesia

Archaeological chronologies use many radiocarbon (14C) dates, some of which may be misleading. Strict ‘chronometric hygiene’ protocols, which aim to enhance the overall accuracy and precision of 14C datasets by removing all potentially problematic samples, mean that so few dates remain in some locations that accurate chronologies cannot be established. 14C dates on charcoal can be affected by an ‘old-wood’ effect, and so they are often removed from analyses, despite >40,000 being available worldwide, representing > $25 million. We show that when a Bayesian chronological model is used, which incorporates an Outlier Model specific to wood charcoal, the 14C dataset of Iceland's Viking Age settlement agrees well with ice core-dated tephrochronology and written sources. Greatest accuracy comes from an even temporal distribution of 14C dates and more dates lead to greater precision (<20 years). This shows how charcoal-based 14C chronologies can pinpoint the transformational human settlement of islands in the Atlantic, Oceania, and elsewhere.This project was funded by the Icelandic Centre for Research (Rannís 121153-0061), Watanabe Trust fund and National Science Foundation (USA, NSF 1202692 and NSF 1249313)

Constructing chronologies in Viking Age Iceland: Increasing dating resolution using Bayesian approaches

yesPrecise chronologies underpin all aspects of archaeological interpretation and, in addition to improvements in scientific dating methods themselves, one of the most exciting recent developments has been the use of Bayesian statistical analysis to reinterpret existing information. Such approaches allow the integration of scientific dates, stratigraphy and typological data to provide chronologies with improved precision. Settlement period sites in Iceland offer excellent opportunities to explore this approach, as many benefit from dated tephra layers and AMS radiocarbon dates. Whilst tephrochronology is widely used and can provide excellent chronological control, this method has limitations; the time span between tephra layers can be large and they are not always present. In order to investigate the improved precision available by integrating the scientific dates with the associated archaeological stratigraphy within a Bayesian framework, this research reanalyses the dating evidence from three recent large scale excavations of key Viking Age and medieval sites in Iceland; Aðalstræti, Hofstaðir and Sveigakot. The approach provides improved chronological precision for the dating of significant events within these sites, allowing a more nuanced understanding of occupation and abandonment. It also demonstrates the potential of incorporating dated typologies into chronological models and the use of models to propose sequences of activities where stratigraphic relationships are missing. Such outcomes have considerable potential in interpreting the archaeology of Iceland and can be applied more widely to sites with similar chronological constraints.British Academy (MD120020) awarded to C. Batt. Rannís PhD funding for M.Schmid.The full text was made available at the end of the publisher's embargo

Multidisciplinary data from Iceland indicate a Viking age settlement flood, rather than a flow or tickle

[Extract] The settlement of Iceland was one of the last acts in a global story of island colonization in prehistory that involved all of earth’s oceans and began deep in history. Understanding the timing and patterns of colonization in general, and the subsequent pace of environmental and cultural changes, is an intensely debated topic in island archaeology (chapters 9 and 10). Was settlement a trickle, flow, or a flood (Edwards 2012)? Debates typically revolve around the accuracy and precision of radiocarbon datasets, as some dates can be older or younger than the associated stratigraphy or archaeological material (chapter 7). Numerous attempts have been made to develop “chronometric hygiene” protocols (after Spriggs 1989; see also chapter 1) to screen data and to eliminate problematic dates. Nevertheless, the criteria used to establish robust radiocarbon chronologies vary around the world (Fitzpatrick 2006; Pettit et al. 2003; Napolitano et al. 2019; Rodríguez-Rey et al. 2015; Schmid et al. 2019; Spriggs and Anderson 1993; Waterbolk 1971)