CONCEPT OF GEOLOGICAL MAP
Definition:-
A map which represent the landform
evolution with relation under layering stratigraphic succession of set of the
rock beds (series).
Geological studies includes the analytical approach in them of
morphology of the surface and
drainage configuration.
Geological
Map
Importance of Geological Map:-
The value of Geological maps for
geography student (particular Geomorphology) need be hardly exaggerated.
1. A geological map shows geographical
distribution of different rocks formation or strata at the ground surface.
2. It’s interpretation leads to an understanding of the lithology
and structure of the under layering rocks.
3. It help in the study of the evolution
of landform in a particular area.
Some Basic Terminology of Geological Map:-
In the beginning it is essential to be acquainted with some salient
features of Geological Map and also with geological terms like Bedding planes,
Dip, Strike, Unconformity etc.
1. Bedding Plane:-
The sedimentary rock are
forms in layers strata or beds the plane that separate two successive beds is
called a bedding plane.
Thus a bed is bounded by two bedding planes
BEDDING PLANE
a. Upper Bedding Plane:-
Which represents the
interface between the bed and overlying younger bed.
b. Lower Bedding plane:-
Which separates the bed
from the from the underlying older bed.The bedding plane may be Horizontal, Tilted,
Folded or Fault in any direction.
2. Dip:-
The inclination of a
bedding plane with respect to the horizontal plane is called it’s Dip.
Unit:-Dip mainly express on degree.(°)
Amount:-Highest amount is 90° (for vertical structure) and
lowest amount is 0° (for horizontal structure).
Types:-Mainly dips are two types
a.True Dip:-Dip measure along the direction of
maximum inclination is called True dip.
b. Apparent Dip:-The dip measure in a direction other
than that of true dip is known as Apparent Dip.
As dip is a
vector Quantity the attitude of bed is show both by it’s magnitude and direction.
The topographical direction in which the
beds dip is called the dip direction.
Formula:-Dip = tan-1 p/b
Where,
P = perpendicular, B= Base
Relation between dip & strike
3. Strike & Strike
line:-
The direction perpendicular to the
direction of true dip is called the Strike and a line drawn in this direction
is called a Strike line.
Unit:-Strike mainly express on kilometer.
Characteristics:-
1. Strike line are represent by the
straight line geological map.
2. All strike lines are parallel to each
other in an ideal geological map.
3. An infinite number of strike line can
be drawn on a bedding plane at varying elevations.
4. The value of strike line are increase
or decrease in a same direction (for
Uniclinal structure).
5. The value of strike line are increase
or decrease in different direction (for Folded
structure).
Bedding plane, contour &
strike line
Method of construction of strike line:-
a. Method - 1
When true dip
direction to represent in Geological Map
b. Method – 2
A contour intersecting a bedding
plane at least at two places
c. Method – 3
More contour intersecting a bedding
plane only one place
4. Unconformity:-
The interruption of a series of beds or
stratigraphic sequence is called Unconformity.
Unconformity Plane:-
The surface separating the two conformable series is known as
the plane of Unconformity.
Importance:-
Unconformity helps to count the number ‘conformable series’ of beds
exposed in map.
1. One unconformity denotes two
conformable series.
2. Two unconformity denotes three
conformable series and so on
Types of Unconformity:-
a. Angular Unconformity:-
Tilted rocks are overlain by flat-laying rocks. Indicates
that during the phase in deposition, a period of deformation and erosion
occurred.
b. Non conformity:-
Metamorphic or
igneous rocks in contact with sedimentary strata. Indicates a period of uplift and erosion of the rocks
previously overlying the igneous/metamorphic
rocks prior to deposition of the younger sedimentary rocks.
Strata on either
of the side of the unconformity.
d. Para conformity:-
An unconformity at which
strata are parallel and the contact is a simple bedding plane.
Comparative
studies of various type of unconformity
Identification
of Geological Map:-
a. Identification of Uniclinal structure:-
In a series when all the
beds dip uniformly in a particular direction, a uniclinal structure is formed.
Visual identification of uniclinal structure-
1.
The bedding planes cut across the contour lines and also curve.
2.
All strike lines are parallel to each other in this structure.
3.
The value of strike line are increase or decrease in a same direction.
4.
The distance of two strike line are always same in this same structure.
5.
Simple Vs can be identified in the pattern of both the bedding plane and
the contours. The relation between the contour-V and the out crop-V
indicates the dip direction and thereby the nature of the valley.
1. When the contour-‘V’ is sharper then the outcrop-‘V’, both pointing in the same direction. The beds dip in up valley direction. (anti dip or obsequent valleys)
2. When the outcrop-V is sharper then the contour-V both pointing in the same direction the beds dip in a down
valley direction. (dip valleys)
3. When the outcrop-V and contour-V
intersect and point in opposite direction the beds dip in a down valley
direction. (dip valleys)
b. Identification of folded structures:-
A fold may either be an
anticline or syncline or a combination of the two.
A fold in which the limbs
dip towards the axial plane is a syncline, and one in which they dip away from
the plane is an anticline.
Visual
identification on folded structure:-
1. Out crop repeat an either side of the
core beds.
2. The ‘V’s of the outcrops combine of from
either ‘X’ or ‘H’ pattern.
3. The bedding planes cut across the
contour lines and also curve.
4. The value of strike line are increase
or decrease in different direction.
5. If younger beds from the core, it is
a syncline.
6. If older beds from the core, it is
anticline.
c. Identification of horizontal
structure:-
When all beds are
parallel with respect of horizontal plane this structure is called horizontal
structure.
Visual
identification of horizontal structure-
1. Contour run parallel two bedding
planes. (this situation it is not possible to
draw any strike line and dip of the bed become zero)
2. On a map it is shown by a plus “+” sign.
3. Younger beds occur higher elevations
and older beds at lower elevation.
d. Identification of unconformities:-
The beds of a single
series of formation are conformable to on other. But in case of two or more series of formations, mutually
unconformable. This is so because they are formed in
different geological age contain beds that differ in attitude, lithological and
succession.
Discordance between any two series of
formation is called an unconformities.
Visual
identification of unconformities-
1. The beds of the younger series appear
to cover the beds of the older series.
2. The bedding planes of the older
series appear to be truncated or to end suddenly.
3. The dip of the bed in two formation
differ.
4. The dip of the different formation usually
intersect.
Unconformity
e. Identification of Intrusive:-
Usually igneous
intrusions are younger than the beds in which they occur.
Conventional symbols for
igneous rocks are used to mark these on maps.
1. Dykes:-Vertical and near vertical intrusion cut across the formation.
2. Sill:-Horizontal intrusions are embedded and run parallel to the
bedding planes.
3. Batholiths:-Batholiths have irregular boundaries and no bedding
plane.
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