GEOLOGICAL MAP INTERPRETATION
Example of Geological and
Topographical maps.
DESCRIPTION OF GEOLOGICAL MAP
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RECOMMEND METHOD
Succession
Structure
Igneous Activity
Geomorphology
History
USES OF GEOLOGICAL AND
TOPOGRAPHICAL MAPS
• Geological map shows the various rock types
in an area.
• Geological map shows geological structures
which are very important in mineral, oil/gas
and underground water exploration and other
engineering works.
• Topographical map shows the physical
features of a place which are very useful in
geological mapping.
THE INFORMATION FROM WHICH
MAP PLOTTING DATA IS DERIVED
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Outcrop exposures
Exposures in cuttings and excavations
Borehole logs
Colour of ant-hills, soils etc.
SCALES
A scale of a map is the ratio between a distance
on a map and a corresponding distance on the
ground.
HOW TO REPRESENT SCALES.
• A scale of a map is always indicated on the
map, and this is done in three(3) ways.
• Verbal scale-This expresses in words the
relationship between a map distance and a
ground distance. Eg. 1cm represents 20m.
• Representative fraction or Ratio scale.
Eg1:20000, 1:50000, 1:125000,etc
• Line or bar scale- this shows directly on the
map the corresponding ground distance.
ROCK STRUCTURE.
• Horizontal strata-They conform to, or run parallel
to the topographic contours.
• Inclined strata-They rarely run parallel to contour
lines. The inclination may be due to either the
deformation of originally horizontal rock units , or
deposition on originally inclined surface.
• Dip-This is the angle of inclination which a line on
the stratum in the dip direction makes with the
horizontal.
ROCK STRUCTURE CONTD.
• Strike- It is a direction which can be measured
and recorded as a compass bearing when part
of the surface of the stratum is exposed to
view. At right angles to the strike is the
direction of maximum slope or dip.
CREATING TOPOGRAPHIC PROFILESTHINGS TO CONSIDER.
• First decide on the line that is of interest to you.
• Pencil the line of your interest on your map. This is the
line of section.
• Place a scaled piece of paper along the line of section.
• Mark clearly, the starting and ending points of the line
of section.
• Make a tic mark wherever the paper crosses a contour
line on the map.
• Connect the dots on the paper, this smooth continuous
curve is the topographic profile.
GENERAL PRINCIPLES OF GEOLOGICAL
MAPPING.
• Preparing to go to the field.
• Things needed.
• Uses of G.P.S(geographical positioning system)
and geological compass.
• Griding of topographical map.
• Difference between traverse, outcrop,
structural and geological maps.
BASIC GEOLOGICAL MAPPING
TECHNIQUES.
• The tasks of a geologist in undertaking
geological mapping of an area include, among
other things:
• The search for useful resources such as gold,
diamonds, underground water or materials for
constructional works.
• The production of a geological map of an area
(this is the main task).
WHAT TO DO AT AN OUTCROP
LOCALITY.
• Date, and areas where traverses will be conducted for the
day
• Put on the G.P.S and take the G.P.S cordinates and give a
number to this locality(this is the locality number of the
outcrop eg.EM001/12)
• Describe the outcrop-massive, weathered. Is the rock fine,
medium or coarse grained?
• Structural features of the outcrop-dip/strike etc.
• Sketch any structural relationships.
• Record samples and photographs taken. Carefully give a
number to the sample(s) taken eg.EM001/1
SOME BASIC LAWS IN GEOLOGICAL
MAPPING.
• The law of superposition
• The law of original horizontality--This law says
that water-laid sediments are deposited in
strata that are almost horizontal and parallel
or nearly parallel to the surface on which they
accumulate.
• The law of original continuity.
• The law of truncation and dislocation.
• Law of cross-cutting relationship.
MAPPING OF AREAS WITH POOR
OUTCROPS-Things to consider.
• Pay attention to excavated areas and road
cuts.
• Pay attention to the colour of anthills and
soils.
• Traverse along streams and rivers.
• Visit hand-dug wells and bore-hole areas.
• Visit high grounds.
PRACTICALS
• Traverse, outcrop, structural and Geological
maps.
• Griding of Topographic map
• Plotting of G.P.S cordinates on topographic
map.
• Plotting of strikes and dips on topographic
map.
• Drawing of sections.