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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