Topographic Maps: - DOC by HC120609004238

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									In the name of God
Shiraz University
College of Agriculture
Department of Desert Region Management

Geomorphology Lab.                       Geological Cross-section:
     Geological Cross-section is a vertical section cutting through the earth
along a straight line on which the layers forming the earth beneath the surface are
shown. On the Geological section also the geological units are shown by the color or
symbols used in the map's legend.
     How the geological cross-section can be drawn schematically based on the
geological map?


      To draw the geological cross
section in a geological map, the
first step is to draw the cross
section line.

      The view direction of on the
cross-section line is shown by the
arrows at the ends of the section
line. What is the view direction?
What will happen if the view be in
the reverse direction?



Layers:
      In order to draw the
geological cross-section, put the
margin of the paper on the section
line. Then draw, the ground surface
line as a line parallel to the section
line on the cross-section paper. If
the topographic map along the
section is available it can be drawn
the topographic cross section along
ht esection line instead of a simple
line.
      Then the intersection
points of the layers
boundary and the cross
section line are extended
perpendicular to the cross
section line to the drown
ground surface.
      The        intersection
points of the layers
boundary with the ground
surface will be determined.




      Now the layer's boundary points on the ground surface must be extended below
the surface in form of a straight line. The boundary line below the ground surface can
be extended in two ways as below:




     The left section is correct in which the boundary lines are drawn so that the
younger formations is located on upward of the older formation in the cross section.
     Based on the given legend, the cross section will be as follow:




    The layer boundaries at the cross-section will be dipping through the younger
formations.


     Based on the given Legend, draw the geological cross-section along LL' line.
Fault:
     If a fault intersects the cross-section line, at first the fault intersection point must
be projected on the ground surface drawn on the section.




       Then the fault point must be extended below the ground surface perpendicular to
it on the section as follow:




      After that the layer boundaries will be drawn based on the discussion given for
the layers section.
Unconformity:
     Specially to draw the cross-section of an angular unconformity in which the
boundary of the unconform layer is not parallel the boundary of the layers located
below it (As can be seen in the following figure), these steps must be followed.
     At first the extension of layer boundaries for the layers located below the
unconformity must be drawn below the unconform layer.




      Tehn put the cross section paper on the map and draw the land surface on
the section in the manner that on the unconform layer outcrop the elevation of the
earth surface be higher. After that the unconfomity boundary must be drawn as
the U line in the following figure.
      After drawing the unconformity boundary (U-line), the boundary of the layers
above the U-line must be parallel to it. And the boundary of the layers below U-line
must be drawn based on the rules discussed for drawing of the layer cross section in
the above mentioned parts.

								
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