Hull G S standard methods for recording Quaternary sediments

(proposals)

(a work in progress)

Genral primciple - it is better to have too much data and edit it later, rather than have too little information and have to repaet the work!

Logging :-

Record the thicknesses of the beds of Till and other deposits that you can see.

Look for structures and sedimentary features. As with all logging pay particular attention to the boundaries between beds - are there signs of erosion. Look also for sheering - caused by the glacier pushing one till over another. This may be associated with other structures such as folding and folding.

For each bed - describe the overall colour, variety of clast sizes, dominant erratics. Also look for and record erratics that you can identify as being from particular locations or geological ages. Pay attention to the textures and shapes of these - are the polished, do they have scratches on them, &c.

When you find elongated erratics in the Till - record the direction of the long axis - this is an indicator of the glacier's direction of movement.

Bulk Sampling -

Collecting samples of the Till and then carrying out lab analysis.

Collect an uncontaminated and un-weathered sample of about 3Kg. Record colour and general appearance when wet. Split into smaller pieces if necessary. Allow to dry naturally.

Samples should be put into clean and preferably new containers and every care taken to avoid the contamination and mixing of samples. A "belt and braces" approach should be used for labeling - labels inside sample and on sample container and in or on any secondary containers!

Sample numbers must be unique, never changed and kept throughout the processing. It does not matter too much what the numbers are and different collectors may use their own system - but changing numbers at a later date is a potential source of confusion. Sub-samples should keep to the same number with an additional bit of information or number - e.g. SAMPLE2-PART or SAMPLE2-2KG or SAMPLE2-ACIDTEST or SAMPLE2>63UM and so on. The sample number may include an abbreviation of the locality name and date collected e.g. SPU6-4#1 (for Spurn June 2004 number 1).

Colour - should be recorded when the sample it thorougly wetted - as samples dry out they become duller in colour. The Munsell Soil Color Chart is an accepted international standard.

Acid test - this will provide an extimate of the carbonate (limestone) content of the sample. Crush a dry sub-sample it into smaller fragments if necessary, remove any large (SIZE?) clasts that would give a biased result, accurately weigh out about 100g of the sample, add to a container of water and then slowly add dilute Hydrochloric Acid (OR SHD WE USE ACETIC ACID?); allow to react, adding more acid if necessary; when reaction is complete add more ware to wash the sample; allow it to settle out, drain off liquid and transfer into a filter paper; allow the residue to drain and then dry naturally; weigh the residue and subtract the weight of the fier paper; then calculate the percentage weight loss. Carbonate content percentage = weight lost/original weight x 100.

Particle Size Anaylsis - weigh out about 1 Kg of the dry sample (more may be needed for fine-grained sediments), add to water and soak it; if clay fraction will not floculate follow microfossil boiling techniques (e.g. Horne 1999) ; wet sieve it at 63um, dry it, sieve it dry into fractions 120um , 250um, 500um, 1mm, 2mm, 4mm [see grain size chart], weigh the fractions and calculate percentages. Tabulate in tables, histograms, pye-charts or graphs.

Do not carry out clast counting or microfossil analysis from these fractions until they have been weighed!

Example--

Clast counting: - identify the clasts in each fraction for statistical purposes - count a random 300+ grains from each fraction if possible. Grains to look for are clear angular quartz, frosted rounded quartz, different colours of quartz, different colours of sandstone, chalk, igneous fragments, metamorphic fragments, heavy minerals, iron minerals, microfossils ...

Be aware of possible sources of bias that could be created during storage - the sediment may get sorted in sample bottles by density or shape (with flatter and lighter clasts rising to the top). Mix up sample again if required before rempving a sub-sample for picking/sorting.

You can also tabulate the percentages of the erratics in the samples -

for the different fractions

There are also methods that you can use to determine the proportion of silt to clay.

Microfossils - pick through the 63 um to 2mm fractions for microfossils (this could be tedious for sandy samples and you may wish to ignore the samller and larger fractions by concentrating on the 120um to 1mm size range. Record and identify any microfossils found. Calculate the percntages of Quaternary and deived microfossils, and percentages of fossil groups found. Many of the deposits will have very few microfossils - so this may only be useful for laminated silt and raft samples.

Be aware of possible sources of bias that could be created during storage - the sediment may get sorted in sample bottles by density or shape (with flatter and lighter clasts rising to the top). Mix up sample again if required before removing a sub-sample for picking/sorting.

Palynology - requies only small samples ca 1 cm square, but suggest keeping 1 inch square so interior is uncontaminated.

Clay mineral analysis - put sample aside for possible future use.

Clay and silt particle size analysis. Particle size analysis can be carried out, but it involves sedimentation rate methods (see Tucker pp 69 to 72) or Centrifugal methods.

Other - Retain at leat 500g of each sample for any future use/study/curation.

Further reading:-

Allman M & Lawrence D F 1972. Geological Laboratory Techniques. Blandford Press, London. 335pp.

Bridgeland D R (ed) 1986. Clast Lithological Analysis. Quaternary Research Association Technical Guide No. 3. 207pp.

Horne M 1999. Starting a small fossil collection. Humberside Geologist 12, 12-17.

McManus J 1988. Grain size determination and interpretation. Chap 3, pp 63-85 of Tucker 1988.

Stow A V S 2005. Sedimentary rocks in the field - a colour guide. Manson Publishing, London. 320pp.

Tucker M (ed) 1988. Techniques in Sedimentology Blackwell Sciemtific Publications, London.

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updated 8/1/6