Friday, December 17, 2010

Features of Rock Outcrops

The distinctly visible features of the rock outcrops are known as planner features of the rock outcrops.Planner
features are important in the study of the structural features of rocks. There are different planner features,
which can be observed in rock outcrops:

Bedding Plane

         The layer which is easily distinguished on the basis of variation in colour, composition and grain
size is known as bed. The plane of this bed or strata is known as bedding plane. It is of fundamental significance
in the study of structural features of sedimentary rocks. The different beds are distinguished from each other by the
difference in mineral composition, variation in grain size or texture, difference in colour and variation in thickness etc.

Foliation Plane

          The segregation of minerals into layers or bands of contrasting mineralogical composition is known as
foliation. The plane of these different bands in metamorphic rocks is known as foliation plane. Foliation plane
is generally formed by dynamo-thermal metamorphism of coarse-grained igneous and sedimentary rocks at progressive
stages of the process. 


          The ruptured surfaces present as cracks in rocks are known as joints. These are the divisional planes
or fractures, which divide rocks into parts or blocks without transverse movement of the blocks. There may or
may not be small movement in the blocks perpendicular to the fracture surface.


          Folds are wavy undulations developed in the surface of the rocks as a result of stresses to which
these rocks have been subjected from time to time. Folds may develop in any type of rock and may be of any shape,
from simple symmetrical up warping or down warping to complex geometrical patterns. The ultimate shape and extent
of folds depend upon a number of factors like the nature, magnitude, direction and duration of forces involved in
the process and the nature of the rocks subjected to such a process.


        An unconformity is defined as a surface of erosion or non depositing occurring within a sequence of rocks.
It indicates a gap or interval of time in the geological history of the area during which the normal process of
deposition was interrupted. It is a structural feature in the sense that rock formations lying above and below it
generally represent different conditions under which they have been formed. Unconformities are recognized in the
field as follows:

·        Visual inspection of the angular relation between the sequences.

·        Presence of Basal Conglomerate.

·        Availability of the residual soil within the sequence of rocks.

·        Exposure of the erosional surface.

·        Contrasting behavior of the rocks from a particular surface.

·        Variation or gap in the geological age of the rocks of the sequence.


          A fault is a planar discontinuity between blocks of rocks that have been displaced past one another in
 a direction parallel to the discontinuity. The faults are distinguished on the basis of following factors:

a) The apparent movement of the disrupted blocks along the fault plane.

b) The relation of the fault attitude (dip and strike) to the attitudes of the

   displaced beds.

c) The direction of the slip.

No comments:

Post a Comment