B A H A N P E L A T N A S

T I M O L I M P I A D E I L M U K E B U M I A N I N D O N E S I A T A H U N 2 0 1 3

PETA GEOLOGI

OLEH :

SAPTONO BUDI SAMODRA

GEOLOGICAL MAPPING

What is a map?

It is a representation of something (Earth, stars, solar system, a building, etc…

What is a geological map ?

A geological map gives information on the superficial layers of the earth‟s crust. The geological formations are listed according to their composition (lithology), their age (stratigraphy) and their structural position (tectonic). They are placed on a topographic base (map) using different graphic elements (symbols, figuratives and colors). The choice of scale depends on the geological content and the intended objective of the map.

A geologic map is an illustration of a huge volume of geologic information. Using a geological map, a geologist can show the distribution of rock bodies at the surface of the Earth and geologic structures which have deformed those rocks.

What is a geological map ?

Geological maps show the occurrence, nature, extent

and stratigraphic age of rock strata in a district

What is a geological map ?

How are geological maps made ?

The essential condition for establishing a geological detail map is a precise field survey, based on numerous measurements and observations. The topographic base is generally taken from maps.

The field geologist determines the rock type according to various criteria and measures its orientation. All data are transcribed onto the map and in a field notebook. Besides the natural or artificial outcrops, data from bore holes or important test holes are taken in consideration

• In the case of a doubtful rock identification, complementary investigations are carried out in the laboratory on samples of these rocks.

• At the end of the field survey, the geologist establishes an original draft at a scale of 1:25'000 and constructs some geological sections across the studied sector. He also writes an explanatory note that generally contains numerous illustrations.

• The geological cartography section assures the direction of the project, carries out the editing of the map, establishes the final legend of the map and provides indispensable data for the cartographers.

How are geological maps made ?

General Considerations

Why make a map? Maps and sections are essential tools in visualising spatial, 3-D

geological relationships. They help with predictions on the location, size, shape and grade of potential ore bodies.

Making or acquiring a geological map is invariably the first step in any mineral exploration program and is a fundamental skill for any exploration or mine geo

Different kinds of geological maps

Large-scale – maps with a small scale ratio 1:1000 or 1:2500. The geo aims to visit and outline every significant rock outcrop in the area of the map. Often called “outcrop” maps.

Small-scale – 1:100,000 or 1:250,000. Only a selection of outcrops are examined in the field and interpolations made between the points. May involve a lot of remote sensing interpretation or projection. Therefore small scale maps are generally more interpretational.

There is always a certain degree of subjectivity in map making, especially in highly weathered terrains where it is difficult to identify the primary rock type

Uses of Maps

To determine where you are going.

To act as a model of Earth‟s surface.

Used to locate various places

To show the distribution of various features or types of materials.

Quick Review of Latitude and Longitude

Latitude

Measured in degrees North and South of the Equator.

Lines drawn parallel to each other running west to east.

Quick Review of Latitude and Longitude

Longitude

Measured in degrees East or West of the prime meridian.

Lines drawn running North and South.

Topography

The lay of the land.

Shows relief using contour lines.

Relief- highs and lows of Earth‟s surface.

Relief can be calculated

Take the difference between the highest point and the lowest.

Ex: Mountain peak 20 m. lake 10m

20m- 10m= 10m

The relief of this area is 10m

Reading a topographic map- Contour Lines

Lines on topographic maps.

Connect points of equal elevation.

Everything connected to that line has the same elevation.

Elevation- the distance something is above sea level. Sea level= 0m or 0ft.

Reading a topographic map- Contour Intervals

Contour interval- gives the difference in elevation between 2 contour lines.

Another indicator of height.

Shown on maps as C.I.= 10ft.

Used to count contour lines.

C.I.= 1000ft

How it will look on a map

Reading a topographic map- Index Contours

A index contour is a contour line that is accentuated in thickness and is labeled with the appropriate measure of elevation.

Index contours occur every fifth contour line.

Help the map user read elevations on a map.

Red arrows indicate location of index contours.

Reading a topographic map- Streams

The direction a streams is flowing is shown on a topographic map by the way a contour line crosses the stream.

Streams are shown as a blue line on maps.

When contour lines cross a stream it looks like an upside down V.

The point in the V points

upstream. It opens in the direction the water is flowing.

Reading a topographic map- Depression Contours

Depression contours show areas of lower elevation.

Drawn like contour lines with marks on the inside.

Hachure marks- tick marks on inside of closed circle.

Reading a topographic map- Hills

Hills are represented on a topographic map by a series of concentric contour lines in a rough circle

Reading a topographic map- Slope

Closely spaced contour lines represent steep slopes.

Widely spaced contour lines represent gentle slopes.

Reading a topographic map- Benchmarks

A benchmark is a place where exact elevation is known.

Shown by a B.M. on map

Ex: BM 60

Reading a topographic map- Colors

The colors on a topographic map are symbolic of different map features. Blue = water Green = forest Brown = contour lines Black = cultural features (buildings, place names,

boundary lines, roads, etc.) Red = principal roads Pink = urban areas Purple = revisions to an older map, compiled from aerial

photos. If an area has become urbanized, this may be shown as purple shading on the new, revised map.

Reading a topographic map- Map Scale

Map scale indicates your distance along the ground, or the amount of ground covered by the map.

USGS- United States Geologic Survey Ratio- 1:24000

one unit on the map is equal to 24,000 units of the same size on the ground. Ex:1 inch on the map = 24000 inches on Earth. Or after converting 1 inch = 2000ft.

Bar scale-indicated by a line or bar with distances marked in miles, feet, or kilometers.

Reading a topographic map- Map Scale

Reading a topographic map- Profiles

A topographic profile is a cross-sectional view along a line drawn through a portion of a topographic map. It is like taking a slice out of a portion of the Earth and

looking at it from the side.

Smart Mapping

Producing a geological map is a process of problem solving. One of the best ways to approach problem solving is known as the system of multiple working hypotheses. This means that the geo doesn‟t start off with a completely blank mind but is armed with a number of ideas about the geology developed from looking at published maps, literature, air photos or aeromagnetics.

Predictions are made, areas are selected and observations are made to test these predictions. It is extremely important to be prepared to discard or modify a particular model or prediction if evidence is found to the contrary. Never fall in love with a particular model or prospect. Good scientific theories are continually being modified or rejected as new evidence becomes available.

Smart Mapping

Systematic mapping vs Smart mapping

Smart mapper will start by looking at aerial photos to determine where the available outcrop is and then make 2-3 traverses across strike to groundtruth the photo interp

Search patterns will focus in on key areas of interest eg shear zones

Less time is spent in areas where the rocks are uniform and a lower density of observations will serve

Most useful observations are the predictable geometrical relationships between bedding, cleavage, lineations and folds as well as movement indicators for brittle and ductile shear zones

Smart Mapping

Observations are not made randomly, nor are they collected on a regular grid according to a fixed search pattern. Rather they are selected to most effectively prove or disprove the current ideas.

Geological mapping is a scientific process and corresponds to the classic scientific method: theorizing, making predictions from the theories and designing experiments (field observations or geochemistry) to test the predictions. (Note: all theories in science must be formulated in such a way that they are capable of being falsified. Eg for field mapping purposes it is not very useful to postulate „these outcrops represent a subduction complex‟ because there is unlikely to be a single observation which can falsify that statement. Rather postulate „this outcrop is basalt and chert, that outcrop is blueschist, that contact is a mylonite…. Together these rocks are thought to have been accreted into a subduction complex‟

LOCATE

A fundamental skill is to be able to correctly position yourself on

your base map

LOCATE – HOW?

•Check grid orientation on map

•Check compass, set declination

•Triangulate (use compass to take

bearings on three prominent

features). Aim for small (< 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 -

LOCATE

On a 1:10 000 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 1:10 000 scale, millimetre accuracy is expected

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?

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.

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

You can put all sorts of things on the map, e.g. where you took a

photograph or collected a sample

Ringed areas of exposure should be moderately coloured; surrounding

unexposed areas should be shaded very lightly with the same colour.

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

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

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

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

STRUCTURAL

DATA

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

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

FEATURE MAPPING

Break of slope used to help locate position of fault (top

left)

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

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)

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

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

These two maps

were produced by

two undergraduates

mapping together

What evidence is

there that they were

working

independently?

Examples of good practice

An exceptionally neat

and detailed map with

a huge amount of

data, many

observations but

without obscuring

critical detail

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’

Examples of good practice

What are the good features of this map?

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)

And how could this map be improved?

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’)

Environmental Sustainability

Ghandi

"Earth provides

enough to satisfy

every man's need,

but not every

man's greed"

ENJOY YOUR MAPPING