GEOL252 Field Studies and New Zealand Geology€¦ · Field Studies and New Zealand Geology Fieldwork Guide 2016 . GEOL 252 2016. Fieldwork Guide. Page 2 of 17 ∞ 1. Keeping a good

Name: ……………………………………

Department of Geology

GEOL252

Field Studies and New Zealand Geology

Fieldwork Guide

2016

GEOL 252 2016. Fieldwork Guide. Page 2 of 17

• 1. Keeping a good field notebook

In many disciplines there is a strong tradition of students keeping field notebooks as a record of their personal commentaries on what they have seen and learned. In geoscience, the commercial geologist’s or geophysicist’s field notebook belongs to the company and not to him or her. Company field notebooks will be fully archived for use by subsequent visitors from the company to the sites recorded. A properly kept field notebook is a document that will stand up in court. It is thus very important that you develop the skill of keeping a good notebook. A field notebook is a permanently bound book, preferably with waterproof or at least water-resistant paper. Field notes must be waterproof and easily maintainable- either pencil or (in good weather) an indelible ink pen (not biro- not waterproof). The notebook should be legible and understandable as written in the field. A day’s work should be reviewed in the evening; at this stage things can be tidied up a bit and colour can be used to help organise and highlight information Do not keep field notes on scraps of paper and then produce a sanitized version in the evening (on the Maerewhenua fieldclass we will collect notebooks from the field). You should include reflections or personalized observations in your field notebook – highlight them by enclosing in a box or cloud-outline shape. If these comments are not written out in the field, identify them with headings like "evening, October 30." Keeping it! It is very important that you keep your notebook safe. Do not lose it. Write your name and address (plus email, mobile number etc) in the front so that if it is found it can be returned. If you are working away from your main address for any length of time, put your local address in the front and indicate the dates you will be at it. Offer a reward to the finder, you will want the book back if you lose it. Photograph new pages of your notebook after each field day so that yo have a back up. Each day Start each day's field notes by writing the date, your location, the weather, your “frame of mind” and any safety matters:

April 1, 2012 Oamaru, Penguin Colony[GR XXXXXX] . Map to show how got here. cloudy but sunny Hazards/safety: from initial view of outcrops- including tide state

It is useful to write a preamble that summarises how you got to the location (e.g. 1 hour drive from Mytown to a car park at Your Bay), , followed by a 30 minute walk to…). Ink or pencil? Whatever you use, your work must be clear enough that it can be photocopied with no loss of detail. Pencils must be sharp and dark. If you use pen, it must be a fine-tipped waterproof ink one. On fine days you may wish to work directly in ink, but continue to do sketches in pencil. Some people ink up their pencil work each day. However, you should only do this if it is necessary to improve the clarity of your pencil work. Don’t create work just for the sake of it!


Style Field notes record your observations. It is not a stenographer's notebook to record what the instructor said. In addition to direct observations, you can pose questions, list things that might help answer those questions, and summarize what you have established up to a point. It is useful to use a set of headings or symbols/icons to separate out different types of information:

Aims

Observations

Interpretation ! Synthesis Brainstorm Summary of someone else’s views (e.g. lecturer)

Diagrams Field diagrams are an essential part of geology field notes. The diagrams are not an end in themselves, they are a useful adjunct to the words and they make you focus. It is a good idea to think of the title of the diagram before drawing it, and write the title down (e.g. view of a fold to show the relation ship between cleavage and bedding). This may help you ensure that you actually draw what you intended to. Field diagrams should also have a scale (scale bar is best) and an orientation (e.g. vertical cliff viewed in direction 270º, plan view with north arrow indicated). They are improved by addition of salient annotations. Be careful to concentrate on drawing the geological relationships using simple clearly defined lines. Avoid giving an “artistic” sketching with wispy line work. Draw what you see- not an idealised picture of what you think it should look like (remembered from a lecture!) Summary Top Tips for a good notebook:

• Organize it. You or anyone else should be able to find information quicky and easily. • Write legibly. If you are messy learn tricks to be neat (write large, use capitals etc) • Write notes. Do not write prose. • Use sketches wherever possible. Sketches have a title a scale and an orientation. • Keep your own observations, your own interpretation, things other people have told

you etc clearly separated. • Set out aims at the start of a day, new location etc. • Summarize at the end of each day, outcrop, thematic set of outcrops. • Set up a notebook index at the earliest opportunity. • Don’t lose it!!!

Good examples To give you some idea of what should be done, the following pages contain examples from a reasonable notebook. Following these is the basic mark scheme we shall use in Maerewhenua.

blah, blah, blah… good idea

synthesis…..


Example of a field day (6) and the start of the next field day


Example pages illustrating synthesis and review of ideas.


Marking scheme for 252 Maerewhenua notebooks. Student Name…………………. Marked by …………………. Marking relates only to work completed on …………………. Are the conditions, state of mind etc clear? 2 marks Have hazards been identified and recorded 2 marks Could someone else find the outcrop easily? 2 marks Is the big-scale breakdown of the outcrop clear? 2 marks Are observations and interpretations clearly separated? 2 marks Bonus marks clear aims and/ or summary Layout of Notebook. 5 marks. Scale:

0. No structure. Impossible to extract information easily. 1. Very little structure. 2. Just enough structure to work out in a few minutes what a particular bit of

notebook relates to 3. Enough structure to work out in a few seconds what a particular bit of notebook

relates to but deficient in some way (prose rather than notes) 4. Excellent but could be improved by……. 5. Excellent

Quality of observations. 5 marks. Scale

0. No useful notes. 1. Very little useful information 2. Observation there but insufficient to characterise reasonably the locality. 3. Basic level of notes to characterize locality. 4. Good notes but some key observations missing. 5. Excellent. No obvious deficiencies

Sketches 5 marks. Scale

0. No sketches. 1. Sketches do not show geologically important info 2. Rudimentary sketches-‐ difficult to see geologically important features 3. Basic sketches that show geologically important features 4. Good sketches that can be improved by……… 5. Excellent. No obvious deficiencies

Marks removed for lack of scales, directions, titles for sketches

Total out of 25……………………………. %


2. Sedimentary Logs (Graphic logs, Measured sections) These comprise: • A graph of the variation of grainsize as a function of height in the section. • Graphic information on lithology, sedimentary structures and forms within units • Graphic information on fossil and trace fossil content, diagenetic alteration etc • Annotations of observations that cannot be incorporated graphically (colour) • Interpretation of sedimentary processes that correspond to particular points on the

section. • Interpretation of sedimentary environments from appropriate facies or facies

associations. An Example:

Top tips for good logs: • Use a Jacob’s staff or tape-measure to measure. • Use a grainsize comparator and a hand lens • Draw what you see- not the textbook example of what you interpret • Interpret process in the field. • Avoid the term energy (high, low, in the middle) in interpretation. There is always a

more precise way of describing process and environment. • Interpret environments in the field. Use all the information you have. • Try to draw up an environmental block diagram.


Base marking scheme for 252 Sedimentary Logs. Student Name…………………. Marked by …………………. Marking relates only to work completed on …………………. Layout: 5 marks

• It should be possible to extract information quickly (in seconds). A five second test will be applied. An interval equal to ~ 50-100mm of column on the graph paper will be selected and examined for five seconds. If the reader can extract:

o The grain size profile and contacts o The rock colour(s) o The nature of any internal structure

Then 3 marks awarded, only two of list 2 marks, one of list 1 mark, nothing from list 0 marks. • Needs name, date, title, location (so that someone can find log locality). All four, 2 marks, three 1

mark, two 0 marks, one -1 mark, none -2 marks. • Columns should be labelled, if not -1 mark • Scale should be clearly marked with numbers and units on the left hand side of the log. If deficient in

any way -2 marks. • Lithologies (information extra to the grain-size profile- e.g. quartz arenite, rather than sandstone -log

dependent) should be clearly marked in the left hand column- either as labels or as colours/symbols with a key. If not -2 marks.

Graphic style: 5 marks

• Grain size range should be appropriate to the log. o 1 mark if max and min on 95% of log less than one unit coarser/finer than reasonable

(observed by staff). o 0 marks if max and min on 75% of log less than one unit coarser/fine and on 95% of log less

than two units coarser/finer than reasonable (observed by staff). o -1 mark if further off than above.

• Grain size profile should be detailed, showing realistic vertical changes (gradual variations and jumps) in grain size. Mark scheme (log dependent):

o 2 marks if profile meets criteria above. o 1 mark if profile a bit simplified. o 0 marks if very unrealistic or if appears to be drawn with a ruler

• Structures and other features should be drawn as they appear (rather than schematically) wherever possible. Structures will be assessed thus (log dependent):

o 2 marks. Log contains abundant realistic graphic detail of relevant structures. o 1 mark. Log contains some realistic graphic detail of relevant structures. o 0 mark. Log contains no realistic graphic detail of relevant structures.

• Writing should be limited to info that cannot be represented graphically. o -2 marks removed if any graphic information repeated in writing or any writing would be

much better as graphic information. Process Interpretations: 5 marks

0. No attempt at process interpretations 1. Attempted to interpret processes 2. One good process interpretation 3. Two good process interpretations 4. Three good process interpretations 5. > three good process interpretations

• -1 mark is any mention of environments in process interpretation column • -2 marks if extensive mention of environments in process interpretation column

Environmental Interpretations:

This is important, but difficult. Will not be assessed at 200 level. Total out of 15……………………………. %


An example of an environmental block diagram


3. Application of the bedform stability diagram: to constrain flow velocity of palaeocurrents Background There is a well-established relationship between grain size of a sediment, the velocity of unidirectional flow over the sediment and the construction of bedforms. Each bedform has a stability field. At insufficient velocities the bedform will not form and at excess velocity the bedform becomes unstable and may transform into another that is stable at that velocity. We are going to apply the concepts in the field. Instructions While logging section through clastic rocks you will routinely estimate the sandstone grain size, using your grain size comparator and hand lens. You use this information to construct the grain size scale on your graphic log. Stability fields for structures that can be linked to bedforms produced by unidirectional flow are shown on the diagram below. (Remember that straght crested or 2D dunes and ripples occupy the lower velocity parts of the respective dune and ripple fields) Your measured grain size and the structure present will enable you to estimate the likely velocity of the current that built the particular structure, back in the Carboniferous! You can record the velocity (as well as the palaeocurrent direction) next to your log and repeat this process for all the structures you observe up the section. Remember, when grain size changes, the same velocity may result in a different bedform being formed.


4. Limestone Classifications Folk

Dunham


5. Stratigraphy in the field In the field it is possible to map distinct rock units, which are indicated in the legend of geological maps with distinct colours and labels. Geological maps show the lateral and vertical relationships between these different units, and geological cross sections interpret these relationships at depth. When you start mapping an entirely new area you have little idea about stratigraphy, but you can identify (or distinguish) lithologies. So initial mapping is always lithological mapping. As you gather more information you may be able to place individual lithological units into a stratigraphic context; mapping will evolve from lithological mapping to litho-stratigraphic mapping. This is a crucial step in many areas. For example an area may contain two lithologically identical sandstones that are of quite different age. Lithological mapping will not distinguish these two units whereas litho-stratigraphic mapping will- giving a more correct analyisis of stratigraphy, structure and geological history. Litho-stratigraphy is a key tool for the field geologist. A geological formation is the major mapping unit defined by a field geologist: it is a mappable litho-stratigraphic unit. That means that it has a defined lithology (or set of lithologies) and can be placed in a stratigraphic column. Formations that are formally recognised are defined in a type locality, where (ideally) the lower and upper boundary are exposed, and where (again, ideally) it is possible to measure a continuous section that makes it possible to describe the formation. Thus formations are named after the type locality (e.g. Taratu Formation). It is useful when defining your own Formations to include the main lithology in the name (e.g. Smith’s Farm sandstone Formation). Formation names may be altered and formations maybe amalgamated when maps of large areas are compiled from individual field maps. In order to summarize big scale data formations can be lumped together into larger units such as groups. Lithostratigraphy is a field tool. There are other stratigraphic approaches that require different tools/ data. Some are listed below and you should find out more about these during the course of your studies.

• Biostratigraphy • Chronostratigraphy • Sequence Stratigraphy

The table on the next page is a chronostratigraphic chart. Where we can, we will tell you the age of rocks we are working on so that you can relate observations you make in the field to the bigger picture of New Zealand Geology:


New Zealand Geological time scale


6. Measurements and plotting of planes and lines

Example of field data plotted on stereonets (from Flint, S.S., Prior, D.J., Agar, S.M., & Turner, P., 1994. Stratigraphic and structural evolution of the Tertiary Cosmelli Basin of southern Chile and its relationship to triple junction evolution. Journal of the Geological Society of London. 151, 251-268.)



Plotting Stereonets- these are excerts from an excellent website: http://www.uwgb.edu/dutchs/STRUCTGE/LABMAN.HTM Plotting planes as great circles

Plotting planes as great circles and poles


Plotting lines as points

Documents

GEOL252 Field Studies and New Zealand Geology€¦ · Field Studies and New Zealand Geology Fieldwork Guide 2016 . GEOL 252 2016. Fieldwork Guide. Page 2 of 17 ∞ 1. Keeping a good