The following article by T. Palmer of the British Museum (Natural History) appeared originally in “The Geological Curator”. It provides a useful guide to the logging of temporary sections and is reproduced here by kind permission of “The Geological Curator”.

As a volunteer digger recently on the dinosaur-dig in Surrey, I was given a pickaxe and told ‘Dig out that corner!’. Two hours later there was no doubt in my mind that recovering large vertebrate fossils, even from ‘soft’ Weald Clay, is very hard physical work; and my usual techy impatience with the vertebrate stratigraphist’s apparent indifference to the minutiae of more amorphous subdued. They clearly had their hands full of more immediate problems than the exact date when the animal lived. Since everyone else was busily applying their special expertise to the dinosaur, I, having done my stint, went off and applied mine to the stratigraphy. But when someone, looking at some 90 ft of varied clays, shales, sands and ironstones, asked ‘Where do you begin?’ it became clear that, if one has never done it before, two procedures much rock can appear rather daunting. The following two procedures are offered as a reply, and directed essential to those with a geological background, but who have never done any ‘on-the-ground’ stratigraphy.

The first procedure is for those rare occasions when time is unlimited and a fairly thorough account can be drawn up in a leisurely manner; when there is time to correct ones mistakes and argue the finer points of lithological differentiation on the ground. The second is for the usual desperate rescue-job, with very little time even to make a mistake and every one saying ‘Come on, haven’t you finished yet?’. Stratigraphy, in a very real sense, is ‘time-consuming’; but this is not always apparent to those who have never done any.

(A) If time permits, the following ‘A-Procedure’ is recommended for establishing a stratigraphical record of any sedimentary geological exposure. It is important to follow the steps in the order given, both for economy of effort and the maintenance of priorities.

  1. Walk all over the pit, or along the length of the exposure, and look at everything; but do not record, measure or collect. Take one or several photographs with a graduated 1 metre scale included. Use your eyes and hand lens and look only, until features become familiar and recognisable. Plunging straight into recording will usually lead to wholesale corrections later.

  2. Roughly sketch the major rock features as they are presented directly to the eye. Use simple descriptive rock terms like ‘grey limestone’ or ‘brown sandstone’, and avoid laboratory terms like ‘micropsarite’. Having established the major units, make rough measurements between them so as to establish the lithostratigraphical framework.

  3. Now go over the sequence again filling in lithostratigraphical details of minor units, still using simple field nomenclature ‘small grey limestone nodules’ and ‘irony concretions with bivalves’ etc.

  4. Go home and study your results. Develop films and make large prints and study them together with written records and sketches. When you are satisfied that photographs and records match, and you can recognise the major division and also the minor units, make another return trip.

  5. Return and measure the succession from minor unit to minor unit; and, at the same time, check the lithostratigraphical nomenclature used previously. You may decide that the ‘brown sandstone’ is better described as a ‘buff-coloured siltstone’. Take a photo of it for parts of the succession and make a note of any and record identification on the print. Clearly identify and record any areas of doubt or uncertainty if, say, part of the succession is obscure, overgrown, or faulted. When you have finished and are satisfied that you cannot improve on the lithostratigraphical succession recorded, then that is the time to assign some sequential notation to each unit recorded; and a numerical notation is preferable to alphabetical. If you cannot decide what to regard as a bed then make each distinct unit a distinct bed and give it a number. Always number from the bottom upwards.

  6. Now is the time to collect fossils from each of the lithostratigraphical units recognised, and to mark each bag or sample with the correct bed notation. It is at this point that even the most experienced stratigraphers can get into a muddle; keep cool and keep checking. When fossil collecting has reached the point of diminishing returns, stop and use the collection to make a biostratigraphical classification and impose it on the lithostratigraphical succession. Here it is wise to procure the help of an experienced stratigrapher, but if none are present then you may legitimately rest on your laurels with your lithostratigraphical recording. At least the basic facts are not lost. However, by studying G.Surv 1” series geological maps of the area, a surprising amount may be learned from them; and, with a 6 figure O.S. map reference, one can pinpoint the locality with surprising accuracy so that it immediately becomes apparent, not only which formation the exposure was made in, but also whether the exposure was near the top or bottom, or roughly in the middle of the formation. Look at the Memoir that goes with the geological map and, if it appears a bit ‘heavy’, try the Regional Guide which will give a very general account of the formation, after which the Memoir may seem less formidable. Already the ‘experienced stratigrapher’ is becoming unnecessary.

  7. In addition one can now collect rock samples from each lithostratigraphical unit, marking each with correct bed notation, for laboratory sedimentological studies. It is easy and quick to collect the samples but very long-winded processing them for study; however, once they are collected, the samples can rest until you, or a sedimentologist, are ready to deal with them. When this is finished you can add the laboratory sedimentological descriptive nomenclature to the field nomenclature:

“Bed 3, Dark grey fossiliferous limestone with irregular top surface: bioturbated microsparite with intraclasts, bioclasts and framboidal pyrite”. Do not abandon the field nomenclature; it is the only way one can recognise rock units in the field.

It is assumed that procedures 1-7 will be distributed over 3 separate visits. This may be regarded as the minimum for reliable results for publication. Some stratigraphers will not publish unless they have made numerous visits over at least six months. Because it is so easy to miss an important stratigraphical horizon in, say, 60 feet of varied lithology, it is understandable why stratigraphers are usually cautious.

(B) If time is very limited and will not permit a full account to be made, then adopt the ‘B-Procedure’, which is designed to concentrate on the essentials and extract the maximum useful information.

  1. Photograph the clearest part of the section with a 1 metre scale in prominent position.

  2. Make a rough sketch of the lithostratigraphical framework, as in 2 of the ‘A-Procedure’, but without details and without measurements.

  3. Collect fossils and rock samples from each unit and put them together in same bag and measure as you go. Ignore smaller units and concentrate on major divisions: it is better to have an overall picture with a few errors, than a detailed account of only the lower.

  4. Work fast and, if you gain time use it to fill in details of minor units. If you are lucky, and the bulldozer breaks down, you may get a second chance. If not you will have a rough outline and scaled photographs which will yield further details. The chances are that no one else will do it and your record will be unique.

  5. On returning home, immediately sort out your written and sketched field records. If you have worked fast there will be corrections and crossings-out, and these are best sorted out while the memories are still fresh. Draw up a clean account, but keep original field notes until you have checked them against enlarged photographs. Add to your finished account the length of time spent working at the exposure so that subsequent workers can judge the probable accuracy of your work. As with the ‘A-Procedure’, it is important to identify and record areas of uncertainty.

If it is uncertain how much time will be available, use the ‘B-Procedure’, then, if there is time, use the ‘A-Procedure’ from onwards. Always work from broad general descriptions to detailed particular descriptions’ if you work the other way around time may catch you out. A camera is a very useful tool in geology - if it is used. Even a poor quality photograph may have a richness of information content, and it only takes about thirty seconds to take a camera out of its case, remove the lens cap, take an exposure reading, focus and press the shutter release and wind on three times.

If time is so desperately short that you have only one photograph and an OS. six-figure map reference, then all is not lost. First, locate your position on the 1 inch OS Series and transfer it to the 1 inch Series geological map. This will tell you not only the formation the site is located on, but also whether the site is at the top, the bottom, or near the middle: “uppermost Oxford Clay” or “middle Weald Clay” is quite a useful stratigraphical fix if no one has anything better. If a photograph shows a mappable geological unit then the chances are it will be mapped on the 1 inch rock series which are often surprisingly detailed. If it is mapped then you have a roughly measured distance on your scaled photograph between the fossil and a recorded and mapped rock unit. Academics may argue about the ‘boundaries of the Callovian’ or the ‘validity of the Aalenian’ but you now know, like Robinson in Pooh Bear, exactly where you are. Serious stratigraphical data is an important part of the scientific information associated with any fossil: collectors and curators neglect it at their peril.

P. Palmer Department of Palaeontology British Museum (Natural History) Cromwell Road London SW7 5BD

Editors Note

The following publication will be found immensely useful when undertaking stratigraphical recording of the kind described by Phil:

TUCKER, M.E. 1982 The field description of sedimentary rocks. London, Open University Press/Halstead Press. 112pp. price £4.95.

References

  • TUCKER, M.E. 1982 The field description of sedimentary rocks. London, Open University Press/Halstead Press.