An R package to analyse, and summarise, multiple radiocarbon (14C) determinations. The package provides two linked (but distinct) Bayesian approaches that can both be used to obtain rigorous and robust alternatives to summed probability distributions (SPDs):
Both methods are implemented using Markov Chain Monte Carlo (MCMC).
The easiest way to install the latest release is via CRAN, by typing the following into your R console:
install.packages("carbondate")
You can alternatively install the development version of carbondate from GitHub with:
::install_github("TJHeaton/carbondate") devtools
Once you have installed the library with either of the above methods, you need to load it using:
library(carbondate)
There are a few example datasets of radiocarbon determinations (e.g.,
two_normals
, kerr
,
pp_uniform_phase
, buchanan
,
alces
, equus
, human
, …) provided,
which can be used to try out the calibration functions.
two_normals
is a small simulated dataset for which the
underlying calendar ages were drawn from a known mixture of two normals.
It is included simply to give a quick-to-run example for the Bayesian
Non-Parametric Density calibration functions.
pp_uniform_phase
is another small simulated dataset, for
which the underlying calendar ages were drawn uniformly at random from a
short calendar interval (equivalent to a single uniform phase). This is
included to give a quick-to-run example for the Poisson Process
modelling functions. The remaining datasets are from real-life data. The
Northern Hemisphere IntCal calibration curves and Southern Hemisphere
SHCal calibration curves are also provided.
The below example implements the Bayesian non-parametric calibration
and summarisation approach on the simulated two_normal
data
using the IntCal20 curve via two (slightly) different MCMC methods.
<- PolyaUrnBivarDirichlet(
polya_urn_output rc_determinations = two_normals$c14_age,
rc_sigmas = two_normals$c14_sig,
calibration_curve=intcal20)
<- WalkerBivarDirichlet(
walker_output rc_determinations = two_normals$c14_age,
rc_sigmas = two_normals$c14_sig,
calibration_curve=intcal20)
Once the calibration has been run, the resultant estimate for the joint (summary) calendar age density can be plotted.
PlotPredictiveCalendarAgeDensity(
output_data = list(polya_urn_output, walker_output),
show_SPD = TRUE)
The
summary estimates generated by the Bayesian non-parametric approach
(shown in purple and green) are called predictive densities. They aim to
predict the calendar age of a future (new) sample based upon the set of
14C samples that you have summarised.
The below example implements the Poisson process modelling approach
using the simulated pp_uniform_phase
data and the IntCal20
curve.
<- PPcalibrate(
pp_output rc_determinations = pp_uniform_phase$c14_age,
rc_sigmas = pp_uniform_phase$c14_sig,
calibration_curve=intcal20)
Once the calibration has been run, the posterior estimate for the occurrence rate of the samples can be plotted.
PlotPosteriorMeanRate(output_data = pp_output)
This estimated rate, and changes within it, can be interpreted
equivalently to methods of calendar age summarisation.