OxCal P_Sequence Model

This option writes the OxCal code for a P_Sequence model. It also conducts an outlier analysis and combines dates at the same depth. For more information see Bronk Ramsey (2008) and Bronk Ramsey (2009). To use OxCal, you must first obtain a password. Click the OxCal online link on the OxCal website to obtain a password or to login to OxCal. See Modern Age Models for instructions for accessing the Export Chron Controls dialog box.

Click the radiobutton for OxCal P_Sequence (*.oxcal) to write the OxCal input file. Select the calibration curve and units for your collection unit. Two methods for obtaining ages for proxy-sample levels are provided. Visit the OxCal website to learn more. Two files are written: the .oxcal file, which contains the OxCal code, and a .csv file that has a list of all sample depths in the data worksheet.

 

The Interpolate option will produce an interpolated age and 95.4% confidence limits at regular intervals down the collection unit. Tilia will suggest a default value for Interval. As a rule of thumb, select an interval that will produce around a 100 interpolated ages, although more interpolated ages for longer collection units may be warranted. The interval value entered is a nominal value, and the actual value will differ somewhat. The parameter entered for the P_Sequence function will be the reciprocal of Interval, which is the number of interpolations per unit length. The interval depths will probably not exactly match your sample depths, but ages and confidence limits can be interpolated for your actual depths as explained below. For most models, the Interpolate option is recommended.

 

The Date function option will produce a full probability distribution function for each sample depth. However, the model will take much longer to run and may not converge with a large number of samples. This option is recommended for only a small number of samples or if the full probability distributions are needed.

After logging in to OxCal, click File > Open to open the .oxcal file saved from Tilia.

The project window will open in the users root directory. In this case, a folder NELSON88 was created for this project, and the new folder was opened. Click the Upload button to upload the .oxcal file written by Tilia.

Click the Choose File button to select the .oxcal file.

After selecting the file, NELSON88.oxcal in this case, click the Ok button.

After the file uploads, highlight the uploaded file name and click the Open button.

The file will open in model view. Click the code view button to see the code.

Click the Run button to run.

A window will appear showing the progression of the run. This may take a long time.

After the run finishes, the results will appear in a table.

To display summary statistics, click Format on the menu to the left of the table and select the desired statistics (μ, σ, Median). You will need to check either μ or Median or both to enter the mean (μ) or median sample ages into Tilia.

 

Also, ensure that the Range 95.4 is checked and that Date reporting is cal BP (yrs).

The drop down menu above the table offers various ways to display the results. See OxCal > Viewing output for more information.

The image below shows a depth plot, which can be saved in various formats under File > Save as. One option is to save as an SVG plot, which is a vector format, which can be manipulated in other graphics programs for making figures for presentations or publications. 

To generate and save ages for each sample depth, click the  symbol to the right of P_Sequence in the table.

The modeled radiocarbon dates and the interpolated dates are displayed in the upper right panel of the Raw data view. If the Date function option was selected, the modeled dates are displayed. To generate interpolated dates for your exact sample depths, open the depths .csv file saved from Tilia in Excel or NotePad and copy-and-paste the depths to the upper left panel. Be sure to include the top row with 'z'. Click the Get dates << button to generate the interpolated dates.

To save the interpolated sample ages, click the Save button.

Click the Download button to download the sample ages to a .csv file.