1
GEOLOGICAL MAPPING
A geologist must remember that accurate
geological maps are the basis of all geological
work, even laboratory work, for it is pointless
to make a detailed investigation of a specimen
whose provenance is uncertain - Barnes Basic
geological mapping.
2
Your indispensable guides Geological Society
handbooks
3
Where will you be mapping?-1

• Semester 2 - Easter one week residential course
  (Leader Prof Eelco Rohling, March 31 April 7
• A series of exercises involving mapping, logging
  and construction geological cross-sections from
  field data. The locality (Tenby, South Wales)
  will also provide an introduction to a wide range
  of rock types and a large variety of field
  relationships, sedimentary and tectonic
  structures.

4
Where will you be mapping?-2

• Summer term weekend May 11 14 (Brittany
  residential field course)
• Basic field skills but in an area of more complex
  igneous and metamorphic geology

5
Where will you be mapping?-3

• SOES 2012 (M Geol, Geology Single Honours,
  Geology with...., MGeoph,GS).
• First summer vacation residential field course
  at Ingleton (Leader Dr D Teagle, - First week
  Summer vacation)
• This course provides basic training in field
  mapping and involves the production of a
  geological map of the Ingleton area.

6
Where will you be mapping?-4

• SOES 2022 (M Geol, Geology Single Honours,
  Geology with....and Geoscience pathway for OESS).
• Easter vacation residential field course,
  Almeria leader Heiko Pälike
• This course provides an opportunity to map, log
  and interpret a variety of different rock
  associations helping to build a comprehensive
  experience of field geology. The focus is
  provided by detailed study of some well exposed
  examples of geological processes. It also affords
  an introduction to fieldwork in an overseas
  environment.

7
SOES 3025/3027 (M Geol, Geology Single Honours,
Geology with....).
Where will you be mapping?-5

• Year 2 Summer term (after semester 2
  examinations) one week course (Anglesey leader
  Dr Dorrik Stow) This completes the core
  component of fieldwork training. It focuses upon
  the challenges of mapping in an area of more
  complex geology where emphasis is placed upon the
  collection and presentation of data and putting
  into practice methods introduced in lectures and
  the laboratory.
• NB OC/GY and OESS oceanography pathway students
  take SOES 3018 (Plymouth). Geophysical Sciences
  students take SOES 3021, Geophysical field methods

8
There is no substitute for the geological map
and section - absolutely none. There never was
and there never will be. The basic geology must
come first - and if it is wrong, everything that
follows will probably be wrong - Wallace (1975)
Mining Engineering, 27, 34-36.
9

• Geological mapping an ability to
• observe and record field data selectively and
  systematically for the construction of a
  geological map at a given scale
• compile a field note book containing an accurate
  record of all field data, including field
  sketches and photographs
• compile field sheets representing a visual
  summary, using accepted conventions, of all the
  mapping data recorded in the field notebook
• construct an accurate and well drafted
  interpretative geological map using conventional
  map symbols
• construct a representative geological section
  across the mapped area
• (Geological Society of London)

10
LOCATE
A fundamental skill is to be able to correctly
position yourself on your base map
11
LOCATE HOW?

• Check grid orientation on map
• Check compass, set declination
• Triangulate (use compass to take bearings on
  three prominent features). Aim for small (lt 1mm)
  triangle of error.
• Pace and bearing. Pace out distance from known
  feature marked on map (use compass to take
  bearing on feature and mark faintly on map so
  line can easily be removed)
• GPS -widely used in industry new course SOES
  2023 next year

12
LOCATE
On a 110 000 map, 1 cm on the map represents 100
m in the field. You should be able to pinpoint
yourself to within 10 m in the field, so when you
translate this to the map, the margin for error
is 1 mm Remember, when mapping at 110 000 scale,
millimetre accuracy is expected
13
OBSERVE
Spend some time looking at the exposure. What is
the rock type? Mineral composition? Grain size?
Texture? What structure can I see? Bedding?
Tectonic fabric? Sedimentary structures?
14
OBSERVE

• Observations are recorded in two ways
• On the field map (field sheet or slip)
• In the field notebook (information which cannot
  be accommodated on the field map see ppt on
  Blackboard - geological field work).
• Map data is also normally recorded in the field
  notebook using a locality number reference system
  on the map and a grid reference in the field
  notebook
• Thus you can navigate between the two.

15
ON THE MAP

• All exposures ringed by a solid line, colour
  coded by formation with an abreviated
  lithological descriptor e.g. f.gr.rd. sstn (
  fine grained red sandstone
• Information about what can seen (can be
  pictorial)
• All structural data, unless there is too much to
  fit it all on the map, in which case,
  representative structural data

16
You can put all sorts of things on the map, e.g.
where you took a photograph or collected a sample
17
Ringed areas of exposure should be moderately
coloured surrounding unexposed areas should be
shaded very lightly with the same colour.
18
RECORDING EXPOSURES

• Map A good features
• Represents exposure shape on the map as
  accurately as possible, bearing in mind the scale
• Accurate placement of boundary due to accurate
  recording of observations
• V effect in valley where boundary is inferred
• Map B poor features
• Exposures too blobby and not to scale
• Boundary poorly placed due to above features
• V effect in valley not interpreted

19
MAPPING TECHNIQUES

• Traversing
• Walking along a predetermined route plotting in
  the geology on the way
• The geology in between traverses is interpolated,
  using whatever clues can be gleaned from the
  topographic map
• This method is used predominantly for
  reconnaissance work
• Large areas of ground can be covered

20
MAPPING TECHNIQUES

• Green line mapping
• Exposures ringed by green lines using a very fine
  (0.1 mm) nib size
• ALL exposures are portrayed. There should be
  evidence on the map that all the ground has been
  covered
• When all exposures have been mapped, boundaries
  between the units can be drawn on the map
• The classic technique for 1 10 000 mapping

Barnes Plate 1
21
MAPPING TECHNIQUES

• Boundary mapping
• One of the main aims in compiling a geological
  map
• Locate a boundary and follow it across the map
• One of the easiest methods of mapping where
  exposure is good
• Very effective in conjunction with aerial
  photographs
• Does not work well if exposure is poor

22
STRUCTURAL DATA
Use compass to transfer reading directly onto the
map, e.g. strike direction Draw appropriate
symbol on map in black ink with fine pen at point
of measurement Indicate dip (plunge) amounts in
figures on map. Record compete data in
notebook Use red ink for faults if possible
23
MAPPING IN POORLY EXPOSED AREAS

• You need to look for and record on the map
  indirect evidence, e.g.
• Soil colour, spoil from man-made holes, fence
  posts, animal burrows
• Float (loose rocks or stones which may reflect
  the underlying bedrock) but be wary of fluvially
  transported material
• Vegetation can reflect underlying bedrock e.g.
  limestones beech, juniper

24
MAPPING IN POORLY EXPOSED AREAS

• Feature mapping
• Map topographic features that may indicate
  underlying differences in the geology
• Use them to help locate boundaries in unexposed
  areas
• Map convex and concave breaks of slope

Convex break of slope, tick on downhill side
Concave break of slope, tick on uphill side
25
FEATURE MAPPING
Break of slope used to help locate position of
fault (top left)
26
BOUNDARIES AND CONTACTS

• Always complete your map IN THE FIELD by drawing
  boundaries between units and extrapolating into
  unexposed areas
• Never leave out a boundary EVEN IF you are
  uncertain where to place it you will probably
  never return to the same spot
• Use the appropriate convention
• Boundary certain
• Boundary uncertain
• Boundary conjectural

27
All field sheets should have a lithostratigraphic
key and all structural symbols used should be
explained. The lithostratigraphic key should
contain information about lithotype (i.e. not
just a list of formation names)
28
Make sure you write your name on the reverse of
each field sheet. The lithostratigraphic key can
be on the reverse A diagram to show how the field
sheets fit together is very helpful
29
Do not keep more than one copy of each field
slip. A field slip is a working document which
should be inked up each night ready for use in
the field the next day
30
SPOT THE DIFFERENCE?
Mapping in pairs You must map independently and
make your own observations We check to see that
you have mapped independently by assigning
markers to mapping pairs
31
These two maps were produced by two
undergraduates mapping together What evidence
is there that they were working independently?
32
Examples of good practice
An exceptionally neat and detailed map with a
huge amount of data, many observations but
without obscuring critical detail
33
Examples of good practice
This coastal map makes good use of free space to
illustrate the style of some of the structures a
picture is worth a 1000 words
34
Examples of good practice
What are the good features of this map?
35

• Good features
• Neatness (Use of capitals for clarity, all text
  written horizontally)
• Annotation of all exposure by lithological type
  (though more detail would be better)
• Annotation of map everywhere ( showing ground has
  been covered)
• Mapping of features to help intepretation (of
  line of fault across top of map)

36
And how could this map be improved?
37

• Many good features but
• Need to annotate ALL exposures to indicate
  lithology (ies) seen (avoid bubbles and numbers)
• Need more information describing what can be seen
  to provide evidence for interpretations (see e.g.
  comment on map Formation thrust forward from
  further south)

38
ENJOY YOUR MAPPING
Campsite bar-restaurant
Cantabrians
Scotland - Kerrera