Geology Reference
In-Depth Information
(see
Basic Geological Mapping by Barnes & Lilse; The Mapping of Geological
Structures by McClay
, from this geological field guide series).
2.3 Notebooks and Data Recording
When preliminary preparations have been completed, the task of working with
igneous rocks in the field begins in earnest. At this stage, it is tempting to rush
up to an outcrop in order to identify rock-types immediately. However, a more
cautious approach is to be recommended.
An important part of any fieldwork is reconnaissance, and 10 - 15 minutes
spent walking round your outcrop and visually taking in its variety and possible
key features, is a far better use of time than to try and immediately take vigorous
notes at an outcrop. Remember to 'recce' your rocks every time as this allows
you to gather your thoughts and prepare to record the information properly.
You should develop a clear structure to your notebooks. It is vitally important
to separate observations from interpretation as well as to record information as
accurately and quantitatively as possible. Record your location (this should be
done using an eight figure grid reference - appropriate GPS position), the date,
the weather and your current mood including a basic statement of your plan.
2.3.1 Field sketches
It is often good to start looking at an outcrop from a larger scale and then work
into the detail, so that all of the key observations can be made. You can start this
by making a general outcrop sketch to which the detailed observations can be
added (for example, Figure 2.2).
Field Sketches
of key outcrops and features are
important as they help to illustrate the processes and structures which have taken
place to form the igneous rocks. Every sketch MUST have a scale and orientation
(direction or field of view), and should be annotated as extensively as possible.
Also record any samples and photos taken (see examples Figures 2.2 and 2.3).
Due to the complex 3D nature of many outcrops, discontinuous exposure and
the relationships you are trying to get across, it may be best to use a
synoptic
sketch
. These 'cartoon' like sketches can be very helpful to summarise the
salient features of your outcrop and can be used to help explain processes, key
relationships and time sequences pertinent to your outcrop. Additionally sketch
geological/outcrop maps can also help put everything into context (for example,
Figures 2.4 and 2.5).
2.3.2 Logging
A powerful way of recording sequences of rock is to produce a log up through
the sequence. A graphic log can be used to record any banded, layered or
bedded sequence of rocks and can be used both in plutonic and volcanic
sequences. This can be done using sketch logs in your notebook (for example,
