Geoscience Reference
In-Depth Information
easiest way to measure a dipping plane with the different
instruments. If this technique is new to you, or the reading
seems unreasonable, or the bedding surface is not ideal,
take a second or even third reading and use the average or the
best one.
Determination of the orientation of a dipping plane
using the clinometer hinge of the Brunton-type
compass-clinometer
You can also use the graduated hinge ('hinge clinometer';
Figure 2.3a) of the Brunton Geo or the Freiberger Stratum
compass-clinometer to measure the dip magnitude. This feature
is cleverly designed so that you can measure both the azimuth
of the dip direction (at 90° to the strike) and the dip magnitude
in one go without needing to move the compass-clinometer to
obtain the two readings (Figure 2.8a). To measure the
orientation of a plane using the hinge clinometer:
2
1. Place the compass-clinometer on the dipping plane with
the back of the mirror part fl at on the plane (Figure 2.8).
2. Keeping the back of the mirror fl at on the plane, rotate the
compass window to the horizontal using the round spirit
level (Figure 2.8a).
3. Note the two readings; the hinge clinometer shows the
magnitude of the dip (Figure 2.8b) and the compass needle
shows the dip azimuth (Figure 2.8c).
The strike can be obtained by subtracting or adding 90° to the
dip azimuth. If you record the strike you will also need the
general dip direction (e.g. east). Note that if you are quoting
dip azimuth rather than the strike it is important to check
that you are not 180° out and to make it clear that this is what
you are recording (see Section 8.1.1 and Table 8.1 for further
discussion).
2.3.2 Orientation of a linear feature
The need to measure the orientation of linear features is
common in sedimentary rocks (Chapter 6) and rocks that are
deformed (Chapter 8). The steps are similar to measuring a
plane except that in this case the orientation of the feature with
respect to north (the azimuth) is recorded by orientating the
long edge of the compass-clinometer parallel to the linear
feature (Figures 2.9 and 2.10, pp.
18-19 and 21). As for a
dipping plane the azimuth should be recorded as a three-digit
number and the plunge as a two-digit number. Alternative
notations for the notebook to that shown in Figures 2.9 and
2.10 are shown later in Table 8.1.
