Non uniform sediment deposition dating
The temporal relationship of "the fill" context to the ditch "cut" context is such that "the fill" occurred later in the sequence; you have to dig a ditch before you can back-fill it.A relationship that is later in the sequence is sometimes referred to as "higher" in the sequence, and a relationship that is earlier, "lower", though this does not refer necessarily to the physical location of the context.The concept derives from the geological use of the idea that sedimentation takes place according to uniform principles.When archaeological finds are below the surface of the ground (as is most commonly the case), the identification of the context of each find is vital in enabling the archaeologist to draw conclusions about the site and about the nature and date of its occupation.The principle of original horizontality states that any archaeological layer deposited in an unconsolidated form will tend towards a horizontal deposition.Strata which are found with tilted surfaces were so originally deposited, or lie in conformity with the contours of a pre-existing basin of deposition.We can also see that if the fill of cut 5 – the wall 2, backfill 3 and trample 12 — are not removed entirely during excavation because of "undercutting", non-residual artifacts from these later "higher" contexts 2, 3 and 12 could contaminate the excavation of earlier contexts such as 9 and 10 and give false dating information. Earth and Planetary Sciences » Geology and Geophysics » "Effects of Sediment Transport on Hydraulic Structures", book edited by Vlassios Hrissanthou, ISBN 978-9-9, Published: December 9, 2015 under CC BY 3.0 license. Based on two case studies, the impact of ice cover on local scour around bridge piers is presented in this chapter.
If one looks at the sequence in fig A, one may find that the cut for the construction of wall 2, context 5, has cut through layers 9 and 10, and in doing so has introduced the possibility that artifacts from layers 9 and 10 may be redeposited higher up the sequence in the context representing the backfill of the construction cut, context 3.
The principle of stratigraphic succession states that any given unit of archaeological stratification exists within the stratigraphic sequence from its position between the undermost of all higher units and the uppermost of all lower units and with which it has a physical contact.
Understanding a site in modern archaeology is a process of grouping single contexts together in ever larger groups by virtue of their relationships.
However the date of contexts often fall in a range of possibilities so using them to date others is not a straightforward process.
If we know the date of context 1 and context 9 we can deduce that context 7, the backfilling of pit 8, occurred sometime after the date for 9 but before the date for 1, and if we recover an assemblage of artifacts from context 7 that occur nowhere else in the sequence, we have isolated them with a reasonable degree of certainty to a discrete range of time.