QUB | Archaeology and Palaeoecology | The 14Chrono Centre

Manual for psimpoll and pscomb

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Menu L: age-depth conversion

Age-depth models may be based on either radiocarbon age determinations (the default) or calibrated ages. Use with radiocarbon ages directly is simpler, and their input is described under Format of associated input files.

Calibrated ages

Use with calibrated ages is more complex, because of the nature of these ages. There is no one-to-one conversion of radiocarbon ages onto a calibrated calendar year timescale. The calibration curve is irregular, and the result of mapping a radiocarbon age, with its symmetrical normal probability distribution, onto the irregular calibration curve is an irregular probability distribution, which cannot be treated statistically in the same way as radiocarbon ages. psimpoll appraoches the problem through the output generated by the BCal calibration system. Other calibration programs are available (see Radiocarbon Web-info), but BCal offers two advantages:

• It uses a statistical approach that makes it possible to take account of other dates during the calibration of each individual date. For example, if it is known that one date is younger then the other, because of their stratigraphic relationship, it is possible to use this restriction to reduce the range of probabilities for calibrating either date. Individual dates can also be calibrated, with essentially the same result as from any other calibration program.
• It provide output in a convenient tabulated form, for further use.

The use of calibrated ages is determined here, in menu L, but some of the details are controlled in menu N, and discussed there.

When menu L is selected, the following submenu appears:

L Conversion of depths to ages
a Convert depths to ages (off)                    [off]
b Specify an age for the top sample               [0+/-50]
c Specify an age for the basal sample             []
d Select an age model                             [1]
e Select number of terms for polynomial age model [0]
f Change laboratory error multiplier (1.00)       [1.00]
g Include timescale with depth axis (off)         [off]
h Convert all ages to AD-BC scale (off)           [off]
i Use calibrated ages from BCal (off)             [off]
j Mode or weighted average with calibrated dates  [MODE]
9 Leave this menu

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