Bacon | R Documentation |
This is the main age-depth modelling function of the rbacon package.
Bacon(
core = "MSB2K",
thick = 5,
coredir = "",
prob = 0.95,
d.min = NA,
d.max = NA,
add.bottom = TRUE,
d.by = 1,
seed = NA,
depths.file = FALSE,
depths = c(),
depth.unit = "cm",
age.unit = "yr",
unit = depth.unit,
acc.shape = 1.5,
acc.mean = 20,
mem.strength = 10,
mem.mean = 0.5,
boundary = NA,
hiatus.depths = NA,
hiatus.max = 10000,
add = c(),
after = 1e-04/thick,
cc = 1,
cc1 = "IntCal20",
cc2 = "Marine20",
cc3 = "SHCal20",
cc4 = "ConstCal",
cc.dir = c(),
postbomb = 0,
delta.R = 0,
delta.STD = 0,
t.a = 3,
t.b = 4,
normal = FALSE,
suggest = TRUE,
accept.suggestions = FALSE,
reswarn = c(10, 200),
remember = TRUE,
ask = TRUE,
run = TRUE,
defaults = "defaultBacon_settings.txt",
sep = ",",
dec = ".",
runname = "",
slump = c(),
remove = FALSE,
BCAD = FALSE,
ssize = 4000,
th0 = c(),
burnin = min(500, ssize),
youngest.age = c(),
oldest.age = c(),
MinAge = c(),
MaxAge = c(),
cutoff = 0.01,
plot.pdf = TRUE,
dark = 1,
date.res = 100,
age.res = 200,
yr.res = age.res,
close.connections = TRUE,
save.info = TRUE,
older.than = c(),
younger.than = c(),
save.elbowages = FALSE,
verbose = TRUE,
...
)
core |
Name of the core, given using quotes. Defaults to one of the cores provided with rbacon, |
thick |
Bacon will divide the core into sections of equal thickness specified by thick (default |
coredir |
Folder where the core's files |
prob |
Confidence interval to report. This should lie between 0 and 1, default 0.95 (95 %). |
d.min |
Minimum depth of age-depth model (use this to extrapolate to depths higher than the top dated depth). |
d.max |
Maximum depth of age-depth model (use this to extrapolate to depths below the bottom dated depth). |
add.bottom |
Add a model section at the bottom of the core, in order to ensure the bottommost date is taken into account. Default |
d.by |
Depth intervals at which ages are calculated. Defaults to |
seed |
Seed used for C++ executions. If it is not assigned ( |
depths.file |
By default, Bacon will calculate the ages for the depths |
depths |
By default, Bacon will calculate the ages for the depths |
depth.unit |
Units of the depths. Defaults to |
age.unit |
Units of the ages. Defaults to |
unit |
Deprecated and replaced by |
acc.shape |
The prior for the accumulation rate consists of a gamma distribution with two parameters.
Its shape is set by acc.shape (default |
acc.mean |
The accumulation rate prior consists of a gamma distribution with two parameters. Its mean is set by acc.mean (default |
mem.strength |
The prior for the memory (dependence of accumulation rate between neighbouring depths) is a beta distribution, which looks much like the gamma distribution.
but its values are always between 0 (no assumed memory) and 1 (100% memory). Its default settings of |
mem.mean |
The prior for the memory is a beta distribution, which looks much like the gamma distribution but
its values are always between 0 (no assumed memory) and 1 (100% memory). Its default settings of |
boundary |
The assumed depths of any boundary, which divides sections of different accumulation rate regimes (e.g., as indicated by major change in the stratigraphy). No hiatus is assumed between these sections, and memory is reset crossing the boundary. Different accumulation priors can be set for the sections above and below the boundary, e.g., |
hiatus.depths |
The assumed depths for any hiatus should be provided as, e.g.,
|
hiatus.max |
The prior for the maximum length of the hiatus. Hiatus length is a uniform distribution, with equal probabilities between 0 and |
add |
Add a value to the maximum hiatus length if a boundary is chosen. Defaults to 100 yr (or whatever other age unit is chosen). Can be adapted if Bacon complains that the parameters are out of support. |
after |
Sets a short section above and below hiatus.depths within which to calculate ages. For internal calculations - do not change. |
cc |
Calibration curve for C-14 dates: |
cc1 |
For northern hemisphere terrestrial 14C dates (IntCal20). |
cc2 |
For marine 14C dates (Marine20). |
cc3 |
For southern hemisphere 14C dates (SHCal20). |
cc4 |
Provide the name of an alternative curve (3 columns: cal BP, 14C age, error, separated by white spaces and saved as a plain-text file). It is important here to first produce a tailor-made folder for your and the default calibration curves to live in. See |
cc.dir |
Directory where the calibration curves for C14 dates |
postbomb |
Use a postbomb curve for negative (i.e. postbomb) 14C ages. |
delta.R |
Mean of core-wide age offsets (e.g., regional marine offsets). |
delta.STD |
Error of core-wide age offsets (e.g., regional marine offsets). |
t.a |
The dates are treated using the t distribution (Christen and Perez 2009) by default ( |
t.b |
The dates are treated using t distribution by default ( |
normal |
By default, Bacon uses the t-distribution to treat the dates. Use |
suggest |
If initial analysis of the data indicates abnormally slow or fast accumulation rates, Bacon will suggest to change the prior. |
accept.suggestions |
Automatically accept the suggested values. Use with care. Default |
reswarn |
Bacon will warn you if the number of sections lies outside the safe range (default between 10 and 200 sections;
|
remember |
Bacon will try to remember which settings you have applied to your cores (default |
ask |
By default Bacon will ask you to confirm that you want to run the core with the provided settings. Disable this using |
run |
In order to load an existing Bacon run instead of producing a new one, you can use |
defaults |
Name of the file containing settings for the core. For internal use only - do not change. |
sep |
Separator between the fields of the plain text file containing the dating information. Default |
dec |
Character for decimal points. Default to |
runname |
Text to add to the corename for specific runs, e.g., |
slump |
Upper and lower depths of any sections of assumed abrupt accumulation, that require excising before age-modelling (and adding after age-modelling). Requires pairs of depths, e.g., |
remove |
Whether or not to remove depths within slumps. Defaults to |
BCAD |
The calendar scale of graphs and age output-files is in cal BP (calendar or calibrated years before the present, where the present is AD 1950) by default, but can be changed to BC/AD using |
ssize |
The amount of iterations to store at the end of the MCMC run. Default 4000; decrease for faster (but less reliable) runs or increase for cores where the MCMC mixing (panel at upper-left corner of age-model graph) appears problematic. |
th0 |
Starting years for the MCMC iterations. These are randomly chosen by default. |
burnin |
Amount of initial, likely sub-optimal MCMC iterations that will be removed. |
youngest.age |
Minimum age limit for Bacon runs, default at current year in cal BP. To set plot limits, use |
oldest.age |
Maximum age limit for Bacon runs, default at 1,000,000 cal BP. To set plot limits, use |
MinAge |
Deprecated - use youngest.age instead. |
MaxAge |
Deprecated - use oldest.age instead. |
cutoff |
Avoid plotting very low probabilities of date distributions (default |
plot.pdf |
Produce a pdf file of the age-depth plot. Defaults to |
dark |
Darkness of the greyscale age-depth model. The darkest grey value is |
date.res |
Date distributions are plotted using |
age.res |
Resolution or amount of greyscale pixels to cover the age scale of the age-model plot. Default |
yr.res |
Deprecated - use age.res instead |
close.connections |
Internal option to close connections after a run. Default |
save.info |
By default, a variable called ‘info’ with relevant information about the run (e.g., core name, priors, settings, ages, output) is saved into the working directory. Note that this will overwrite any existing variable with the same name - as an alternative, one could run, e.g., |
older.than |
an option to enable dates at the limit of C-14 dating. If there are older.than dates, they tell us that the core should be older than a certain age at that depth. For example, if the 7th and 8th dates in the core's .csv file are older-than dates, use as |
younger.than |
an option to provide younger-than ages, for example a historical pollen marker. If there are younger-than dates, they tell us that the core should be younger than a certain age at that depth. For example, if the 7th and 8th dates in the core's .csv file are younger.than dates, use as |
save.elbowages |
If you want to have a file with the MCMC-derived ages for all the age-depth model's elbows, set |
verbose |
Provide feedback on what is happening (default |
... |
options for the age-depth graph. See agedepth and calib.plot |
Bacon is an approach to age-depth modelling that uses Bayesian statistics in order to reconstruct Bayesian accumulation histories for deposits, through combining radiocarbon and other dates with prior information ('Blaauw' and 'Christen', 2011).
Bacon divides a core into many thin vertical sections (by default of thick=5
cm thickness),
and through millions of Markov Chain Monte Carlo (MCMC) iterations estimates
the accumulation rate (in years/cm; so more correctly, sedimentation times) for each of these sections.
Combined with an estimated starting date for the first section, these accumulation rates then form the age-depth model.
The accumulation rates are constrained by prior information on the accumulation rate (acc.mean, acc.shape
) and its
variability between neighbouring depths, or "memory" (mem.mean, mem.strength
). Hiatuses can be introduced as well, also constrained by prior information (hiatus.max
).
Although Bacon works with any kind of absolute dates (e.g., OSL, tephra or other dates on a calendar scale),
it is often used to age-model 14C-dated sequences. Radiocarbon dates should be calibrated using either IntCal20
(for terrestrial northern hemisphere material; Reimer et al., 2020), Marine20 (for marine dates; Hughen et al., 2020),
SHCal20 (for southern hemisphere dates; Hogg et al., 2020) or any other calibration curve (see below), while modern 14C
dates are calibrated using one of the post-bomb calibration curves (NH1, NH2 or NH3 for the northern hemisphere,
SH1-2 or SH3 for the southern hemisphere; Hua et al., 2022). See http://calib.org/CALIBomb/ if you are unsure which
postbomb curve you need. If Bacon finds postbomb dates (negative 14C ages) and you haven't specified a postbomb curve,
you will be prompted. Provide postbomb curves as, e.g., postbomb=1
for the NH1 postbomb curve (2 for NH2, 3 for NH3, 4 for SH1-2, 5 for SH3).
For calendar dates, i.e. dates that are already on the calendar scale and thus should not be calibrated, setcc=0
.
Since version 3.1.0, rbacon can also handle younger-than and older-than ages, with the model aiming to either go 'above' or 'below' such dates as requested. If the resulting combination of parameters becomes problematic (e.g., no initial combination of parameters can be found that obeys the priors or is in chronological order), then the output will often be wrong. If so, using the function set.initvals could help.
By default, the initial MCMC values of the Bacon age-depth model (upper ages and accumulation rate for each model section) are estimated randomly. Since version 3.1.0, these starting values can also be provided in a file with extension _bacon.init, placed within the core's folder. This file will need to have two rows, each for one of the two initial sets of parameters required (the t-walk requires two starting estimates for all MCMC parameters). If such a file is found (and correctly formatted), Bacon will use the values within this file as starting points for the MCMC run. See function set.initvals for more information.
From version 2.5.1 on (i.e., since February 2021), the default memory prior has changed to mem.mean=0.5
and mem.strength=10
. Previously used c++ code contained a bug which caused the prior information for the memory not to be
taken into account correctly. Now that this bug has been repaired, the default memory prior has been updated such that it should work
for most types of cores, and should result in similar output to previous versions of Bacon. There is no need to re-do previous runs.
However, it is considered good practice to test the impact of different settings on a site's age-depth model
(e.g., thick, acc.mean, acc.shape, mem.mean, acc.strength).
An age-depth model graph, its age estimates, and a summary.
Maarten Blaauw, J. Andres Christen
Blaauw, M. and Christen, J.A., 2011. Flexible paleoclimate age-depth models using an autoregressive gamma process. Bayesian Anal. 6(3): 457-474.
Christen, J.A., Perez E., S., 2010. A new robust statistical model for radiocarbon data. Radiocarbon 51: 1047-1059.
Reimer et al., 2020. The IntCal20 Northern Hemisphere radiocarbon age calibration curve (0–55 cal kBP). Radiocarbon 62(4): 725-757. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1017/RDC.2020.41")}
Hogg et al. 2020 SHCal20 Southern Hemisphere calibration, 0-55,000 years cal BP. Radiocarbon 62(4): 759-778. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1017/RDC.2020.59")}
Hughen et al. 2020 Marine20-the marine radiocarbon age calibration curve (0-55,000 cal BP). Radiocarbon 62(4): 779-820. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1017/RDC.2020.68")}
Hua et al. 2022 Atmospheric radiocarbon for the period 1950-2019. Radiocarbon 64(4), 723-745, \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1017/RDC.2021.95")}
Jones, V.J., Stevenson, A.C., Battarbee, R.W., 1989. Acidification of lakes in Galloway, south west Scotland - a diatom and pollen study of the post-glacial history of the Round Loch of Glenhead. Journal of Ecology 77: 1-23.
Bacon(ask=FALSE, coredir=tempfile())
Bacon(cc=2, delta.R=80, delta.STD=40, coredir=tempfile())
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