fg lecture 3 field measurements and techniques

Field Geology2010-2011

Ibrahim M.J. Mohialdeen,MSc,PhD

Lecture 3

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Subject: Field measurements and Techniques

* lecturers name: Ibrahim M.J. Mohialdeen* Contacts: Tel: 0770 142 6262, Email: [email protected]

*Subject objective: The instruments which are used in the geological procedures during field works are very important and the geologist should be experience with them. In this lecture you will learn how to measure dip and strike of beds and how to plot them on the map. The plan of the first trip on Thursday will be discussed.*Scientific content of the subject:Strike and dip of bedsMeasurementsPlotting methodsFolds , faults and jointsField trip No.1 Guide lines

*Subject references:- Mikhailov,A.Ye.,1987, Structural geology and geological mapping, Mir Publishers, Moscow, 535p.- Compton, R.R., 1962, Manual of Filed Geology, John Wiley and Sons, New York, 378p.- Barnes, J.W., 1995, Basic Geological Mapping, 3rd ed., John Wiley and Sons, Chichester,

133p. Field Geology 2010-2011

Field measurements and techniques

Lecture 3:

Field measurements and techniques

Measuring strike and dip: Strike: it is the direction of the intersection

of the surface with any horizontal plane. Dip: it is the maximum angle of slope of

the surface. The dip is an angle in a vertical plane and must always be measured downward from the horizontal plane. The direction of dip is perpendicular to the strike. Field Geology 2010-2011

Method 1: Contact method, this is the commonest of all. Use it where the surface to be measured is smooth and

even.

Field Geology 2010-2011

Method 2: This method is largely used for unevenplanes of relativelylow dip. Estimate a strikeline a meter or more long, then stand over it withyour compass opened out and held parallel to itat waist height.

Method 3: This gives reliable measurements of strike and dip in regions where large areas of moderately dipping bedding planes are exposed or where surfaces are too uneven to measure in any other way.


Method 2


Method 3

Measurement of dip Measurement of StrikeField Geology 2010-2011

Method 3


Plotting strike and dip:

Plot strike and dip immediately you have measured them. Use the way pencil-on-point (POP) (after Barnes, 1991). It takes only a few second , as follows:

1-Place your pencil on the point on the map where the observation was made ( Fig a).

2-Use your pencil as a fulcrum and slide your protractor along it until the origin of the protractor lies on the nearest north-south grid line; then still keeping the protractor origin on the grid, slide and rotate the protractor around your pencil still further, until it reads the correct bearing (Fig b).

3-Draw the strike line through the observation point along the edge of the protractor (Fig. c).


Plotting strike and dip:


The Silva compass has the advantage that, if used according to the directions enclosed with it, you can use the compass itself as a protractor. Make your

reading, then without disturbing the setting of the rotating graduated ring, align the N-arrow inscribed on the transparent base of the compass case with the

grid line and slide it into position ( Fig. ).


Recording strike and dip:Right-hand rule:Strikes and dips must be recorded in a manner where there can be no possible confusion over the direction of dip; the recording of dip 180 in error is a common mistake( after Barnes, 1991).Recording may be as follows:Write bearing of the strike, followed by a stroke, and then the amount of dip and the quadrant it points to: Example: 223/45NW or S43W/45NW.The right-hand rule is simpler; always record strike in the direction yourright index finger points when your thumb points down the dip ( Fig. ). The quadrant letters can now be omitted and the reading of 223/45NW now becomes 043/45. All types of planar information can be written in this form.

The right-hand rule for recording strike and dip(Barnes, 1991).

A lineation is defined in space by its trend; the bearing of an imaginary vertical plane passing through it- and by its inclination or plunge in that plane( after Barnes, 1991).

Measuring linear features:Linear features related to tectonic structures are termed lineations.


Some lineations appear as lines on an inclined surface . These inclinations can often be measured more easily by their pitch (rake), that is, the angle the lineation makes with the strike of the surface on which it occurs.

Measuring linear features:


Folds:some of the considerations must be kept in mind.If the axial plane of a fold is vertical , then the crest and

hinge lines are coincident and the trace of axial plane indicates its strike whether the fold plunges or not ( Fig.a). If the fold is overturned , the axial plane is no longer vertical and the hinge line now becomes a lineation formed by the intersection of two surfaces- the inclined axial plane, and the vertical plane in which the trend of hinge is measured( Fig.b)( after Barnes, 1991).


Fold


Faults


Thrusts and unconformities:Joints:

Joints occur in every type of rock, sedimentary,pyroclastic,plutonic ,hypabyssal,volcanic and metamorphic.

Record joints ,but do not clutter your map with them.

Measure the strike and dip of joints in the same way as bedding. Book readings in your notebook, using right-hand rule, together with estimates of joint lengths.


Disconformity:Tertiary, Libya


Field Trip No.1Guide lines


Field Trip No.1

Studied area:Sulaimani, Roadcut .

Aims: Measuring, recording and plotting strike and dip, Finding location on the map.

Date: Thursday /11/2010Time: 8:00am-1:00pm


Field checklistThe following is a list of field equipment. These

items on the list are needed for this field trip:RucksackMap case, NotebookPens, pencils, protractor and erasersBase Map, Hammer, HandlensCompass, Abney level, rod, Field acid bottle, Hat,

Waterproof anorak, Water bottleTape, Camera, Lunch box!

Good Luck

Field Trip No.1 Field Geology 2010-2011

fg lecture 3 field measurements and techniques

Documents

field measurements

field works

field geology2010

direction of dip

plotting strike

strike line

structural geology

plot strike