ShellChron: Builds Chronologies from Oxygen Isotope Profiles in Shells
Takes as input a stable oxygen isotope (d18O) profile measured in growth direction (D)
through a shell + uncertainties in both variables (d18O_err & D_err). It then models the seasonality
in the d18O record by fitting a combination of a growth and temperature sine wave to year-length chunks of
the data (see Judd et al., (2018) <doi:10.1016/j.palaeo.2017.09.034>). This modeling is carried out along a sliding window through the data and yields estimates of
the day of the year (Julian Day) and local growth rate for each data point. Uncertainties in both modeling
routine and the data itself are propagated and pooled to obtain a confidence envelope around the age of
each data point in the shell. The end result is a shell chronology consisting of estimated ages of shell
formation relative to the annual cycle with their uncertainties. All formulae in the package serve this
purpose, but the user can customize the model (e.g. number of days in a year and the mineralogy of the
shell carbonate) through input parameters.
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