Oxcal - D model for varves

[lewis howell]

Hi all, 

Trying to run a D depositional model for a varved lake sequence. Varves are not continuous and are essentially floating (they occur within the full core but do not run from 0 cm downwards). 4 radiocarbon ages and able to run a U model quite easily but cannot get a D model to run. I keep getting a message saying the z value hasn't been defined (which I assume is depth). I am including the depth in the model parameters when setting it up but I am still get the same error message. 

Does anyone have any ideas or pointers? 

Thanks. 

[Erik Marsh]

Hi Lewis,

Yes, z is depth. For a D_Sequence, you have to define known gaps between dates (usually for tree rings). You might actually want a P_Sequence, I'm guessing. Check out the manual's section on sequences. You may be able to include all of the varves in a single P_Sequence, if they all are on a single depth scale. If doesn't matter if they don't start at 0. If not, you can modeled the 'floating' pieces separately and then use cross-referencing to tie them together. If you post your code it will be easier for the forum to help

Cheers, Erik

[lewis howell]

Hi Erik, 

Sorry for the delayed response work is a bit manic at the moment. I am unsure what model is best to use as I know the number of laminae between the radiocarbon dates but the sequence is quite complexed. Essentially, I have a radiocarbon age right beneath the start of laminae formation and there are roughly 300 laminae following this before they cease forming and are replaced by unconsolidated organic material. This continues for the next 40 cm. Within this 40 cm section there is another radiocarbon sample. Above this section of unconsolidated OM laminae begin to reform and continue for the next 80 cm with another radiocarbon date right at the top of the laminae (to determine when they stop forming). 

Essentially the laminated section is floating and fragmented. It is not continuous but stops forming for around 40 cm. Therefore, I can count up from the start of the laminae by calendar year quite easily but this is then followed by a large section of OM where we have a radiocarbon date from. Laminae then reform above this non laminated section. Luckily, given where the mid core radiocarbon date is from I can again count the laminae up until they stop forming and there is another radiocarbon age. I am going to try running a P and D model this week and will update the group. 

Thank you for all your help so far

Lewis. 

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