Terminus ante quem

[Pablo Mendez-Quiros Aranda]

Hi everyone.
I need to run a model that includes a terminus ante quem (TAQ). Reviewing the manuals, the former "TAQ" command is now "Before ()". Oxcal runs the MCMC but ends before reaching 100% done and convergence.
The table contains the model data but the graph is not generated. I copy the code below.
I take advantage of asking how I include in the model a constraint for all the data or for only some.
Thank you very much for the help.

 Sequence("")
 {
  Boundary("1");
  Sequence()
  {
   Phase()
   {
    R_Date("UCIAMS-235989", 350, 15);
    R_Date("UCIAMS-232625", 360, 15);
    R_Date("UCIAMS-232626", 645, 15);
    R_Date("D-AMS 030640", 384 , 33 );
    R_Date("D-AMS 030641", 549 , 26 );
    R_Date("D-AMS 030642", 343 , 23 );
    R_Date("D-AMS 030644", 559 , 23 );
    R_Date("D-AMS 030645", 521 , 30 );
    R_Date("D-AMS 030643", 404 , 26 );
   };
   Before(C_Date("Tefra",1600));
  };
  Boundary("2");
 };

--

Pablo Mendez-Quiros Aranda

Universidad Autónoma de Barcelona.
              

[Erik Marsh]

Hi Pablo,

Your code runs fine. You can simplify it slightly so it runs better, but the results are identical in the code below.

You had a sequence within a sequence; I removed one of them. I changed the Before command to a simpler Date command. Since this is place in sequence after the phase, it fulfills the same function in practice (there is a very minor difference, but I can't recall it right now – does someone else know?).

If this tephra is from the Huaynaputina eruption, don't forget to use a different calibration curve. Possibly SHCal, but a safer bet is a mixed SHCal + IntCal curve – this is what I used here.

As for your second question, I think you would want to do multiple sequences that cross-reference the tephra, but you'll have to tell us what relationships you want to model. You may also be able to improve the model with more information on the relationships between the radiocarbon dates, if they from the same layers over overlaying depositions, etc, especially because you have a few dates sitting on a flat spot in the calibration curve where you get bimodal probability distributions.

Hope this helps

Erik

 Sequence()

 {

  Curve("IntCal20","IntCal20.14c");

  Curve("SHCal20","SHCal20.14c");

  Mix_Curve("Mixed","IntCal20","SHCal20",U(0,100));

  Boundary();

  Phase()

  {

   R_Date("UCIAMS-235989",350,15);

   R_Date("UCIAMS-232625",360,15);

   R_Date("UCIAMS-232626",645,15);

   R_Date("D-AMS 030640",384,33);

   R_Date("D-AMS 030641",549,26);

   R_Date("D-AMS 030642",343,23);

   R_Date("D-AMS 030644",559,23);

   R_Date("D-AMS 030645",521,30);

   R_Date("D-AMS 030643",404,26);

  };

  Date("Tefra",1600);

  Boundary();

 };

[Christopher Ramsey]

The only difference is that with the Before command the Tephra is not assumed to be part of the phase so will affect the end boundary and more minor effects elsewhere.

Christopher

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