The process of geological mapping requires integrating a number of field
techniques. On this page an overview is given on how some
of these techniques have been applied in the Boxgrove Raised Beach
Mapping Project.
3.
Where overlying sediment depths made trial pitting impossible, boreholing was
used to log the distribution of each stratigraphic unit. Boreholing was carried
out using a 5m Dando Rig geared to cut a 150mm hole. Boreholing is a low-impact
method of investigation, leaving only a small re-turfed area of disturbance.
4.
Gravels and loose, unconsolidated, sand were sampled directly from the cutting
as bulk samples. Where the fine-grained, archaeologically sensitive deposits
of the Slindon Formation were encountered, U100 samples were taken. These recovered
450mm lengths of intact, uncontaminated sediment sheathed in 100mm wide piping.
U100 samples are subsequently split, with one half being logged and sub-sampled
and the other half stored as part of our sediment archive.
1.
Familiarity with local topography and landforms can be a useful guide to what
may be present below the ground. Here, in Halnaker Park, the ruined Manor was
sited on the top of a low rise, elevated from the lower, flatter land to the
south. This break in slope coincides exactly with the position of the fossil
cliff cline. It can be traced, as a landform, for much of the length of the
raised beach.
2. Geophysical sensing can be used to provide images of the sub-surface geology.
Here a 400m resistivity array is being set up across an area of ground thought
to contain the fossil cliff line. As each lithology has different conducting
properties, the array can detect stratigraphic boundaries by determining variations
in resistance. Subsurface images help our research by indicating suitable
locations for boreholing.
