1. 4B. Outcrop_Pattern_Cross-Section_Profiles
We have seen how both the land surface and a geological surface can be represented by contour maps. The line on a geological map represents the contact of two formations by marking the intersection of two parallel surfaces.
10. Exercise: Generating a topographic profile
The line emanating east from well 7 is the surface trace of the strata penetrated by the well, projected up dip (see Line L next page), thereby marking were gray beds seen in the well should intersect land surface. Six gray beds (G1-G6) are identified in the borehole and projected up dip.
The same projection of the penetrate interval is applied for a well at 4ICR
The form of the gray beds on the map can be predicted knowing the dip of the beds and the topographic contour patterns, since along the line of intersection both surfaces will have equal height.
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2. Profile geometry of water well penetrating dipping beds
bedding
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3. 10. Exercise: Generating a topographic profile
Outcrop Pattern 1; Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
A rule to remember: A geological surface crops out at points where it has the same height as the ground surface.
10. Exercise: Generating a topographic profile
This grid was constructed using rectangles from the drawing menu. The width of each rectangle is the horizontal distance (~162’) that the formation falls 20’ in elevation, the same vertical distance as the topographic contours.
From Rider/PDFs/Geology & Topgraphy.PDF
Contour spacing (D) = (contour interval / TAN (dip)
D = 20’/tan 7o = 20/0.123 = 162’
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4. Outcrop Pattern 1; Maple Springs Rd to Indian Creek Dr
Outcrop Pattern 1; Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
4. Use the grids or the engineering ruler to complete the outcrop pattern for gray beds G1, G4 – G6. G2 and G3 are given as examples.
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5. Drawing vertical cross-sections through topographical and geological surfaces Vertical cross-sections represent the form of the topography and geological structure as seen on a ‘cut’ through the earth. This vertical cut is imaginary rather than real, so the construction of such a cross-section usually involves a certain amount of interpretation.
The features displayed in the cross-section are the lines of intersection of the section plane with topographical and geological surfaces. Where contour patterns are given for these surfaces the drawing of a cross-section is straightforward. If a vertical section is to be constructed between the points X and Y on Fig. 2.13, a base line of length XY is set out. Perpendiculars to the base line at X and Y are then drawn which are graduated in terms of height (Fig. 2.13B). Points on the map where the contour lines for the surface intersect the line of section (line XY) are easily transferred to the section, as shown in Fig. 2.13B. Provided the vertical scale used is the same as the horizontal scale, the angle of slope will be the correct slope corresponding to the chosen line of section. For example, if the surface being drawn is a geological one, the slope in the section will equal the apparent dip appropriate for the line of section. If an exaggerated vertical scale is used, the gradients of lines will be steepened and the structures will also appear distorted in other respects. The use of exaggerated vertical scales on cross sections should be avoided.
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6. Topographic Profile 1 Maple Springs Rd to Indian Creek Dr
Topographic Profile 1 Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
a. For the line of section A-A’, that crosses the 6 gray bed sequences, generate a set of ruled lines spaced 20’ apart, parallel to the section trace, and relative to a base elevation, in this case 300’.
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7. Topographic Profile 1 Maple Springs Rd to Indian Creek Dr
Topographic Profile 1 Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
b. Raise lines perpendicular to the base line from the section trace to the topographic height of the 20’ contour line that is crossed.
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8. Topographic Profile 1 Maple Springs Rd to Indian Creek Dr
Topographic Profile 1 Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
c. Connect the end points of the raised reference lines using <AutoShapes> <Line> <Freeform> to produce a curve representing the topographic profile
10. Exercise: Generating a topographic profile
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9. Outcrop Pattern 1 Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
d. Raise reference lines from the base line where the gray beds cross the trace. Use the arcs of circle or ellipse to project the lines into section.
10. Exercise: Generating a topographic profile
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10. Cross section 1 Maple Springs Rd to Indian Creek Dr. , Alexandria Twp
Cross section 1 Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
e. Draw in the gray beds using <Autoshapes> <Lines> <Frreform> polygons with semitransparent gray shading. Double right click on the object of choice to access <Format Autoshape>. The first click will access a Move or Copy menu, the second will access <Cut>C<Copy> <Paste> and <Edit Points>, the latter being used to adjust the polygon vertices and thereby refine their shape. Wells are added as ’ deep lines. SW NE
700
Elevation (Mean sea level – ft)
-100
-500
-900
PROFILE VIEW
Objects rotated 31o Clockwise
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11. Cross Section 1 Maple Springs Rd to Indian Creek Dr. , Alexandria Twp
Cross Section 1 Maple Springs Rd to Indian Creek Dr., Alexandria Twp., Hunterdon County, NJ
f. The completed profile. Some ancillary notation and dashing the base elevation line (300’) makes it look more presentable. It is also important to have both the A-A’ and directional (SW – NW) labels and note the profile view.
Alexandria Township, Hunterdon County, New Jersey
A SW
A’ NE
6o apparent dip
MAPLE SPRINGS RD
700
INDIAN CREEK RD
18,16,15
300
Elevation (Mean sea level – ft)
-100
Red beds
Gray beds
-500
-900
PROFILE VIEW
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12. Topographic Profile 2. Hope to Jenny Jump Mt
Topographic Profile 2. Hope to Jenny Jump Mt., Warren County, New Jersey
Print the map on the following page and generate a topographic profile using a base elevation of 400’
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13. Topographic Profile 2. Hope to Jenny Jump Mt
Topographic Profile 2. Hope to Jenny Jump Mt., Warren County, New Jersey
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14. Topographic Profile 2. Hope to Jenny Jump Mt
Topographic Profile 2. Hope to Jenny Jump Mt., Warren County, New Jersey
The orange grid is composed of 100’ high rectangles that are grouped and rotated 318o
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