As a trivial example, a sample taken from between two layers securely dated to 1066 and 1087 will have exactly the same chronological constraints as a sample which is simply known to have come from the reign on William the Conqueror. Both cases can be treated as a sequence of: one securely dated event 1066; the item in question (perhaps with a radiocarbon date of 950BP+-30) and finally another securely dated event 1087. In terms of a stratigraphic diagram we might draw this as:
Sequence { C_Date 1066; R_Date 950 30; C_Date 1087; };The implications of such a simple sequence are fairly obvious in that the original probability distribution for the radiocarbon date will simply be truncated at the two dates 1066 and 1087. The value of analysis only becomes significant in more complicated situations where the implications of the stratigraphic information are not so obvious.
A very important point must be made which is that radiocarbon often do not directly date the context itself and so a naive use of stratigraphic information to refine the dating of the objects can be quite wrong. As an example sample A in pit 1 may be older than sample B in pit 2 even if pit 2 is older than pit 1.
The taphonomy of a site must be carefully considered in constructing a chronological stratigraphy from the physical stratigraphy.
In general the relative order of all samples is rarely known but various stratigraphic groupings can be defined.
Phase { R_Date 2700 30; R_Date 2800 35; };This might then be part of a sequence.
If the samples form a coherent group then they should be enclosed within Boundaries.
See also [Program Operation] [Warning] [Example]
Sequence { R_Date "A" 2760 35; Phase { R_Date "B" 2700 30; R_Date "C" 2800 35; }; R_Date "D" 2660 35; };The stratigraphic information from most sites can in fact be written solely in terms of nestings of phases and sequences. However, to use sequences properly an understanding of Boundaries is needed (see Steier and Rom 2000 and comments on that paper). In this program it is also possible to define a minimum gap between two events in a sequence so that you might have:
Sequence { C_Date 1066; Gap 10; R_Date 950 30; C_Date 1087; };(Please note that in this manual and for this program sequences are always written in the order old to young although they can be displayed in reverse order for consistency with physical archaeological stratigraphy).
See also [Program Operation] [Example] [Warning]
As an example in the case given above we might have:
Sequence { Boundary Start; Sequence { R_Date 800 35; Phase { R_Date 750 30; R_Date 800 35; }; R_Date 660 35; }; Boundary End; };Any coherrent group of events should be contained within boundaries in this way in order to signal that they all belong to one period.
See also [`Using boundaries]
D_Sequence { R_Date 2760 35; Gap 30; R_Date 2910 30; Gap 30; R_Date 2870 35; };See also [Program Operation] [Example] [Warning]
V_Sequence { R_Date 3000 35; Gap 30 20; R_Date 2910 30; Gap 30 20; R_Date 2870 35; };See also [Program Operation] [Example] [Warning]
Sequence { R_Date 980 35; TPQ { C_Date 1066; }; R_Date 930 30; };See also [Program Operation] [Example] [Warning]
Sequence { R_Date "A" 900 30; R_Date "B" 830 35; }; Sequence { R_Date "C" 940 35; TPQ { XReference "A"; }; R_Date "D" 890 70; };Such use of references should be used with caution and combinations of sequences and phases used where possible.
See also [Program Operation] [Warning]
The taphonomy of a site must be carefully considered in constructing a chronological stratigraphy from the physical stratigraphy.