Wednesday 1 March 2017

Concept of Geological map - what is geological map?

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.      Its 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 its 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 its 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, BBase

                                                         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.    Method3
      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 seriesof 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.
                             
c.    Disconformity:-
       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 Vs of the outcrops combine of from either Xor Hpattern.
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.
                               
                                                                                         Folded structure
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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