Usinf After in a sequence

[Chris Chinnock (Chris)]

Hi all, 

Im looking for some help with a model I am putting together for a couple of features dated to the early Roman period (Britain). 

The key bit Im not sure I have built right is the second sequence (Tank). This is a wood-lined tank, which after having fallen out of use, was backfilled and then pits were subsequently cut. A nice little stratigraphic sequence. We have a dendro date which has suggested a felling date of late AD76. We also have a date fromt he backfill deposits (FTMC-QG69-32), and a date from one of the later pits (FTMC-QG69-31). I have attempted to model this but am not sure if I have done so correctly (see code below). I ran the model, and it seemed to work but the agreement was coming through as 0.0%. 

I'd be grateful if someone could take a look and let me know where I have gone wrong. 

Cheers

Chris 

 Plot()
 {
  Sequence()
  {
   Boundary("Spring start");
   Phase("Upper spring")
   {
    Sequence()
    {
     R_Date("SUERC-132244 (1574)",1725,24);
     R_Date("SUERC-132245 (1261)",1730,24);
    };
    Sequence("Tank")
    {
     After("1620 Felling")
     {
      Date("1620",76);
     };
     R_Date("FTMC-QG69-32 (1635)",2113,30);
     R_Date("FTMC-QG69-31 (1631)",2091,30);
    };
   };
   Boundary("Spring end");
  };
 };

[John Meadows]

dear Chris

the only problem I can see is that both the samples from the stratigraphically later contexts appear to be older than the tank. This is not an OxCal problem, rather a question of archaeological interpretation - how long had that material been hanging around before it was deposited where you found it? i.e. where did the fill of the later contexts come from? How can you be confident that organic remains in that fill are not redeposited from much older layers? if, as you say, the tank was deliberately backfilled, the risk of dating residual material must be fairly high - although you might not notice if it wasn't older than the tank itself. 

best regards

John

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[Chris Chinnock (Chris)]

Thanks John, 

Yes, I think there must be some residuality here. 

Chris