17/11/2014 Geology IN: The field notebook

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The field notebook

Field Notes

The field notebook forms the main record of the data you gather in the fi eld. In particular, it should contain notes on where the data were collected, the relationshipsbetween the different rock bodies, their compositional and textural characteristics, and internal features. It usually also records the location of any samples collected, theposition and orientation of any photographs taken, cross references to published information and notes on any ideas that you have for interpretation or questions raised byyour observations. In addition the fi eld notebook usually links together any other components that you might have used to record data and ideas in the field. For instance,an electronic database held on a piece of geophysical equipment, fi eld maps, annotated fi gures and graphic logging sheets.

Your notebook should be kept as neat and well organised as possible. The location of the section being examined should be given precisely, preferably with a gridreference and possibly a sketch map too, so you can find it again in years to come. If you have a GPS, this can give you a very precise location. You may wish to numberyour localities sequentially and put the numbers on a topographic map. You could use the pinhole method – make a hole in the map with a pin and write the localitynumber on the back.

Relevant stratigraphic information should also be entered in the notebook if you know it: formation name, age, etc. It is easy to forget such things with the passageof time. Incidental facts could be jotted down, such as the weather or a bird seen, to make the notebook more interesting and jolt the memory about the locality whenlooking back through the book in years to come. Notes written in the field book should be factual, accurately describing what you can see. Describe and measure wherepossible the size, shape and orientation of the features as discussed and explained in later chapters of this book. Also record the structural data if the rocks are dipping orthere are folds and cleavage present. Note major joints and fractures and their orientation, and any mineralisation. Make neat and accurate labelled sketches of features,with a scale, and orientation, such as direction of north.Record the location and subject of photographs in the notebook. When taking photographs do not forget to put ina scale. Photomosaics of cliffs and quarries can be very useful for extensive exposures, and they can always be annotated directly or with an overlay.

One attribute of sediments which cannot be recorded adequately on a graphic log is the geometry of the bed or the rock unit as a whole Sketches, photographs anddescriptions should be made of theshape and lateral changes in thickness of beds as seen in quarry and cliff faces. Binoculars can be very useful for observing inaccessible cliffs and as a preliminary to closerexamination. Local detailed mapping and logging of many small sections may be required in areas of poor exposure to deduce lateral changes. A GPS can be useful here toget accurate locations of outcropsand even to get the dimensions of features.

(a) Visit to a working quarry to collect rock samples. (Notebook of Angela L. Coe, The Open University, UK.)

(b) Field trip to Snowdonia, UK with introductory notes. (Notebook of Tiffany Barry, The Open University,

UK.)

A checklist of the main points to be covered in the description of a locality in a field notebook:

1. Locality details: location, locality number, grid/GPS reference; date and time; weather.

2. Stratigraphic horizon and age of rock unit, structural observations (dip, strike, cleavage, etc.).

3. Lithology/mineralogy and texture: identify and describe/measure.

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17/11/2014 Geology IN: The field notebook

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4. Sedimentary structures: describe/measure, make sketches and/or take photographs.

5. Palaeocurrent measurements: collect readings and plot rose diagram.

6. Fossils: identify and make observations on assemblages, orientation, preservation, etc.

7. Construct graphic log if appropriate, and sketches of lateral relationships.

8. Note location of samples and fossils collected.

9. Identify facies present, note facies associations and repetitions.

10. Determine/measure rock units and any cycles in the succession.

11. Make appropriate interpretations and notes for future work (e.g., in the lab).

Field sketches: A picture is worth thousand words

Sketches form a vital part of all geological fi eld notebooks. They include: diagrams of cliffs or quarry faces; sketches of individual features such as a fossil, mineral orsedimentary structure; sketch maps; cross - sections; and sketches showing ideas for interpretation.

Part of a graphic log (Notebook of Angela L. Coe, The Open University, UK.)

Sketches are one of the best ways of recording and conveying geological information. This is for two reasons: (1) They provide a shorthand means of conveyinginformation in an easily accessible form. For example, it is much quicker to draw the form of an irregular contact between two beds than to describe it. Because geology ismostly about the relationship between different rock bodies and their three - dimensional geometries, irregular shapes and contacts are common, and it is much easier toconvey this in detail in a figure than it is in words. (2) The very act of producing a good sketch involves carefully observing the features, units and the relationshipbetween all of them. If executed properly, sketches can convey much more of the key geological information than a photographbecause the author has to pick out the important geological features that relate to the objective of the fieldwork more clearly, add labels to show where other data havecome from.

A few coloured pencils are useful for sketches in the field and for distinguishing different parts of the field notes geological field sketch is a combination of a simpleline drawing of the relevant geological features you can observe and your initial geological deductions. Thus photographs are not a replacement for sketches because theyare neither selective nor deductive and you cannot add labels and cross references. Professional geologists regularly use a combination of photographs and sketches.Producing field sketches is the notebook skill that most students of geology and even some professionals find very difficult, but it is a skill that is well worth developing.and add a certain amount of interpretation.

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