Deposition models for chronological records

Abstract

Long term sedimentary sequences provide a wealth of useful information for research into the palaeo-environment, especially in relation to past climate change. Shorter records provide similar information in many archaeological contexts. However if such records are to be used to provide precise timing of events, and more critically the relative timing between different records, methods are needed to provide accurate and precise age-depth models for these sequences. Given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence. Even with layer counted chronologies, the uncertainties are sometimes hard to quantify. This paper outlines a range of Bayesian models for deposition which have been implemented in the computer programme OxCal. These models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information. Such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research.

Combined 14C Analysis of Canvas and Organic Binder for Dating a Painting

“…Data evaluation was performed using the AMS data reduction program BATS (Wacker et al 2010a). Calendar ages were determined using the OxCal v.4.2.4 software (Bronk Ramsey 2008) and the post-bomb atmospheric NH1 calibration curve (Bomb13NH1) (Hua et al 2013;Reimer et al 2013). The resulting calibrated time intervals correspond to 95.4% probability and are expressed in years cal AD.…”

The freshwater reservoir effect in radiocarbon dating

“…The dating results are reported as conventional 14 C dates in 14 C yr BP [43]. Calibrated dates have been obtained using OxCal version 4 with IntCal09 [44,45] and are quoted as cal AD/BC. For the sediment core, an age model was calculated based on 13 radiocarbon dates on macrofossils of unequivocally terrestrial origin.…”

“…To account for changes in accumulation rate, boundaries are inserted at 447, 552, 1055 and 1748 cm, based on major changes in the CaCO 3 content (Figure 2). The age model was constructed using the P_sequence depositional model in OxCal 4.1 [44], with k values between 10 and 200. The final k value of 150 yielded an agreement index of 73.3%.…”

Climatic imprint of the mid-latitude Westerlies in the Central Tian Shan of Kyrgyzstan and teleconnections to North Atlantic climate variability during the last 6000 years

“…Also, one radiocarbon age from the base of the sediment sequence (Poz-44072) was rejected as it turned out to be c. 300 years older than that of another sample (Poz-48597) from the same stratigraphic level, most likely owed to re-deposition of the dated material. In consequence, the age model for composite profile SONK_11_D1/2 (Figure 4) was finally established using the remaining 22 corrected conventional radiocarbon ages (Table 1) as well as the chronological fix points at 5.5 cm sediment depth (first occurrence of 241 Am: ad 1950) and at the sediment-water interface (date of the coring campaign: ad 2011) as input parameters for a P_Sequence deposition model implemented in OxCal 4.1 (Ramsey, 2008). The high agreement index A model of 94.2% proves the robustness of the chronology (Ramsey, 1995(Ramsey, , 2001, which is furthermore independently constrained by pollen analyses, revealing the first appearance of (most likely long-distance-transported) Juglans pollen at 44.5 cm composite depth, i.e.…”