Embedded Files
Taking clear and concise field notes at a rock outcrop is a very important skill. Such data are used as a the basis interpretation. In regular fieldwork, your notebook needs to record what you did each day (even things that seem obvious at the time, as you will forget them) at the time, and include all your observations, supported by sketches. Good marks are given to notebooks that are well laid out, legible and contain copious sketches and diagrams. You may not fully understand all of the detail presented at each outcrop, but might see a clearer example or additional material that lets you understand it later. It is important to try and put pieces together as you go.
In a virtual excursion, most sites will have been chosen for you by the excursion designer. However, you should try and follow the general guidelines below with respect to analysing and interpreting outcrop imagery that is presented for the excursion. Detailed pictures of outcrops may be presented for key rock outcrops, and you should make a sketch of each image and annotate it. As you will not be in the field, you may not need a notebook and can use loose pages but ensure that anyone reading the notes can work out establish their purpose, scale and location
Put your name and contact details on the front page of the notebook. Place a date and page number in the top right corner for each page. Have a consistent layout to the page, such as ruling a column on the left and/or right for location, photograph and sample numbers, along with structural measurements. Use symbols to distinguish structural measurements (S0 for bedding, S1 for cleavage/foliation, L01, L10 for lineations). Put a box around or underline important text (use different colours). For example, different groups of structural measurements may be highlighted or even written in a different coloured pen/pencil. Start each new day on a new page with the day and date. Describe what you are planning to do each at the start of the day.
Kata tjuta
Aim to do as many detailed and labelled sketches each day as you can. When completing regular fieldwork, always sketch of everything that you photograph, as it is very easy to forget why a photograph was taken. Sometimes, it helps to take photographs of memorable images or events (morning tea) to jog your memory. Make a short note as to why you have made a sketch to remind yourself of the importance of the sketch and the key relationship you are trying to show. Add short notes about the outcrop that you sketch and mark where any samples are taken. Use colour to highlight key features in your sketch. Make sure each sketch is labelled with a title, location (grid reference), scale and orientation (north arrow or a ‘view towards’ direction for sketches of vertical sections).
Be prepared for mistakes to be made and be willing to cross these out, rather than wasting time erasing things.
Don’t be afraid to think into your notebook and flesh out, for example, alternative interpretations that you are considering, or summarise the information that might distinguish between different explanations of an observation. These records will be useful when you come to build a final interpretation. Make sure that you indicate clearly what is observation and what is interpretation.
You may have some information which is not recorded in your notebooks or on your maps. This could include such things as stereogram plots, logged sections, and cross-sections. Look after these and hand them in with your notes. Consider making a quick sketch version of these in your notebook with a note pointing to the availability of a higher quality version on loose paper.
It is difficult to decide which data will be critical to your interpretation of the geology of your area while you are in the field so collect as much information as you possibly can.
Checklist for recording information in your field notebook
Location
A six figure grid reference should be recorded. A description of the position of the exposure and a sketch map may be needed.Lithology
Colour What is the colour of the rock? Is there a difference between the colours of the weathered and fresh surfaces?
Grain sizes Record the range of sizes present.
Minerals present Identify the main minerals present in the rock.
Rock type Identify the rock type or types present. If a sample is collected it should be numbered and the number recorded in the field notebook. Describe any peculiarities or characteristics of the rocks.
Sedimentary structures
Record the dip and strike of the bedding
Are the bedding planes evenly spaced or not. Is the rock thinly or thickly bedded? Are the bedding surfaces planar or undulating or irregular?
Other sedimentary structures Describe any other sedimentary structures, e.g. cross-bedding, channels, ripples, sole-markings, concretions, etc., which may be present. Sketch these features. Record the dips and strikes of cross-bedding and the trends and plunges of any linear structures.
Tectonic structures
Foliation Record the dip and strike of planar structures such as schistosity or banding of gneiss or mylonite.
Cleavage Record the dip and strike of slaty or fracture cleavage.
Joints & Fractures Record the dips and strikes.
Faults Record dip and strike and direction and amount of movement.
Folds Sketch the folding and record the trend and plunge of fold axes .
Lineation Record the trend and plunge of lineations such as cleavage–bedding intersections or preferred orientation of elongate minerals.
Other minor structures Note the presence of any other structures such as tension gashes, slickensides, etc., and the direction of movement implied.
Junctions
Many rock exposures have more than one rock type present. Note the distribution of the rock types in the exposure - e.g. conformable, disconformable, cross-cutting -and the nature and orientation of the boundaries. These relationships are crucial to establishing the relative age of the rock units.
Other Note any other obvious features, e.g. mineralisation, relationships of different rock types to each other, etc.
Sketches As well as sketching individual features, larger-scale sketches illustrating the structure of the rocks or relating the geology to topography are necessary.
Until you have developed a routine of examining rocks in the field you should copy this list into your field notebook as a reminder of features to look for and measure.
Some reference diagrams
Some reference diagrams
Igneous Rocks
Igneous Rocks
A QAPF diagram is a double ternary diagram which is used to classify igneous rocks based on mineralogic composition. The acronym, QAPF, stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)". These are the mineral groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized (recalculated so that their sum is 100%).
Sedimentary Rocks
Sedimentary Rocks
Sediment grain size chart.
Classification of siliciclastic rocks based on the four compositional components quartz, feldspars, lithics, and matrix (modified from Williams, Turner, and Gilbert, 1982).
Roundness and sphericity
Degree of sorting
Bouma sequence
The Bouma sequence specifically describes the ideal vertical succession of structures deposited by low-density (i.e., low sand concentration, fine-grained) turbidity currents. The Bouma sequence is divided into 5 distinct layers labelled A through E, from bottom to top. Each layer described by Bouma has a specific set of sedimentary structures and a specific rock type (see below), with the layers overall getting finer-grained from bottom to top. Most turbidites found in nature have incomplete sequences - Bouma describes the ideal sequence where all layers are present.
The layers are as follows:
E: Massive, ungraded mudstone, sometimes with evidence of trace fossils (i.e., bioturbation). The Bouma E layer is often missing because the fine fraction was all moved further away with the current or it has been scoured by a subsequent current. This layer may be difficult to differentiate from the Bouma D layer below.
D: Parallel-laminated siltstone.
C: Ripple-laminated fine-grained sandstone. Often the ripple laminations are deformed into convolute laminations and flame structures.
B: Planar-laminated fine- to medium-grained sandstone. The base of Bouma B often has features known as sole markings, such as flute casts, groove casts and parting lineation.
A: Massive to normally graded, fine- to coarse-grained sandstone, often with pebbles and/or rip-up clasts of shale near the base. Base is sometimes eroded into underlying strata.
Structural Symbols
Structural Symbols
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