Analytical Methods:Coring
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Contents |
[edit] Coring and test pitting
| Scale | Field technique though samples can be used in subsequent laboratory analyses |
| Questions | Coing is useful in site prospection, finding and identifying the "natural", gaining a foresight of deposits before excavation, and studying transects of soils and deposits across landscapes. |
| Time and cost | Depends on the the number of sampling points, however, in some situations it can help reduce the cost of subsequent excavation. |
[edit] Questions
Coring and test pitting are commonly used in prospection studies, particularly in deep sediment sequences to help locate anthropogenic deposits and buried ground surfaces.
Example case studies of coring and test pitting projects include:
- Identify buried anthropogenic deposits
- Identify former buried landsurfaces
- Retrieve samples from deeply buried deposits
[edit] Sampling
Before starting a coring programme ensure that the location of any underground pipes and cables is known.
The sampling pattern and frequency depends very much on the reason for the coring exercise and the nature of the deposits. For example, it may be possible to prove that the natural has not yet been reached with a single core if that core shows the presence of artefact containing deposits lower in the profile. Site prospection and catena studies generally require a more systematic approach employing grid and cross contour transect surveys. The number and spacing of sampling points will be a function of the scale of the landscape and the size and frequency of the features you are hoping to find. Topographic and soil and geology maps can provide a good basis for identifying appropriate sampling units. Depending on the nature of the study there is often a constraint on the number of samples that can be taken in areas where there may be delicate archaeological deposits.
When deep cores (multiple core samples) are required with near perfect depth resolution the usual protocol is to take two adjacent cores (no more than 20 cm apart), which overlap by half the length of the individual core samples. This allows the two cores to be matched together and the potentially disturbed ends of each sample can be ignored.
The U.S. EPA provide a users guide to soil sampling (non-archaeological) on their website that might be useful, available at http://www.epa.gov/esd/cmb/research/bs122.pdf, however the actual decision over any sampling scheme must be made on a case by case basis.
Samples for further analysis can be taken at the time of coring, having first cleaned the surface of the core thoroughly, or the core can be stored (semi-circular plastic guttering can be useful for this) to allow specialists to take their own samples. Each core section must be labelled with its sample point, depth and orientation.
[edit] Coring methods
The equipment available for coring (or test pitting) ranges from a simple spade to sophisticated hydraulic systems.
Coring equipment includes corers (gouge augers) and augers (Dutch or screw augers):
- Dutch (Edelman) auger – principally for collecting disturbed samples from heavily rooted areas (top soils) this is a good tool for geochemical prospection studies, but can also be used in other areas where a disturbed sample is acceptable. Samples from different depths can be laid out to produce a reasonably good picture of the whole profile. The smeared surface of the sample should be cut away before the sample is examined or described.
- Gouge auger (core sampler) – produces an undisturbed sample and gives a more complete picture of the profile with better depth control than a Dutch auger. Generally they are most suitable for use in soft soils and peats though more robust versions are available. The smeared surface of the sample should be cut away before the sample is examined, described or sub-sampled.
- Screw augers – good for use in hard, rocky, or compacted soils, but produces a very disturbed sample.
- Russian corers – these are side filling producing undisturbed, non-compacted samples. They are usually used for coring peat for pollen analysis but are not suitable for soil sampling.
Mechanical corers are also available and are good for producing large numbers of deep cores or for coring very compact or hard soils and sediments. Though they are themselves very heavy and have to be moved between sampling points.
