Geological maps (Dipping Beds) The upper surface of a dipping shale bed (200 m thick) appears at point F. The true dip direction and the angle of this bed are shown on the map. It overlies a 100 m thick sandstone bed and underlies a 100 m thick conglomerate bed. The whole succession is covered by basaltic sheet. 1. Draw outcrops of the beds. 2. Construct two cross sections passing through point F, one is normal and the other is perpendicular to the strike lines. 3. Draw a columnar section with scale of 1 cm=50 m. 4. Determine the true thickness of all beds. 5. Calculate the depth after which the lower surface of the sandstone bed is reached at point Z. (Modified after Al-Tahlawy 1998) 13
Transcript
Geological maps (Dipping Beds)
The upper surface of a dipping shale bed (200 m thick) appears at point F. The
true dip direction and the angle of this bed are shown on the map. It overlies a 100 m thick sandstone bed and underlies a 100 m thick conglomerate bed. The whole succession is covered by basaltic sheet.
1. Draw outcrops of the beds. 2. Construct two cross sections passing through point F, one is normal and the
other is perpendicular to the strike lines. 3. Draw a columnar section with scale of 1 cm=50 m. 4. Determine the true thickness of all beds. 5. Calculate the depth after which the lower surface of the sandstone bed is
reached at point Z. (Modified after Al-Tahlawy 1998)
13
Geological maps (Dipping Beds)
The upper surface of a limestone bed crops out at point A. The amount of dip is 26o. The scale is 1 cm = 100 m.
1. Complete the limestone outcrop. 2. Determine the true thickness of the limestone bed. 3. Draw a geological cross section along X-X'. (From Gokhal 1987)
14
Geological maps (Dipping Beds)
The lower surface of a limestone bed, with a vertical thickness of 200m, appears at point "A". This bed is underlain by a shale bed and overlain by a 100 m sandstone. The Whole succession is caped with basalt. (1) Draw the bed outcrops. (2) Draw Geologic cross section along X-Y (3) What are the main topographic features on the map. (4) Draw a stratigraphic column with a vertical scale of 1cm=50m.
15
Geological maps (Dipping Beds)
Some parts of the upper surface of a 100 m thick conglomerate bed appear on the map, while part of the lower surface of the same bed appears at point C. This bed is underlain by a 200 m thick shale bed that is in turn followed by a 100 m thick sandstone bed. The whole succession is covered by basaltic sheet.
1. Draw all the beds outcrops. 2. Construct a geological cross section A-B. 3. Determine the true dip direction and its amount. 4. Determine the true thickness of all beds. 5. Calculate the depth at which the upper surface of the conglomerate bed is
reached at point Z. (Modified after Al-Tahlawy 1998)
16
Geological maps (Dipping Beds)
Deduce the dip and strike of the coal seam which is seen to outcrop at points A, B and C. At what depth would the seam be encountered in a borehole sunk at point D. Complete the outcrops of the seam. Would a seam 200 meter below this one also outcrop within the area of the map?
Hint: An average coal seam is in the order of five feet in thickness.
(From Bennison 1973)
17
Geological maps (Dipping Beds)
Scale: 1 cm = 200 m
The lower surface of a 100 m thick sandstone bed appears on points A, B and C. It is underlain by conglomerate and overlain by shale.
1. Determine the angle and direction of the true dip.
2. Draw the outcrops of these beds.
3. Draw geological cross section along X-Y.
18
Geological maps (Dipping Beds)
The lower surface of a 100 m thick limestone bed appears on points A, B and C. This bed is underlain by shale and covered by basaltic sheet. Draw the outcrops and construct cross section X-Y.
Scale 1:10000
19
Geological maps (Dipping Beds)
The upper surface of a shale bed appears at points A, B and C. 1. Determine the direction and amount of dip. 2. Draw the beds outcrops according to the vertical thicknesses shown on the
legend. 3. Draw a cross section X-Y.
(From Al-Tahlawy 1998)
20
Geological maps (Dipping Beds)
The lower surface of a sandstone bed appears at points A and B, its upper
surface appears at point C at depth of 100 m, the vertical thickness of such a bed is 300 m it overlies a shale bed (200 m thick) and underlies a conglomerate bed (200 m thick) that in turn covered by basaltic sheet.
1. Draw the beds outcrops. 2. Construct a cross section X-Y. 3. Determine the true thickness, amount and direction of the true dip of
these beds. 4. Calculate the depth at which the lower surface of the shale bed appears
at point N.
21
Geological maps (Dipping Beds)
A 200 m thick shale bed, its upper surface appears at points A and B. The
lower surface of this bed is reached at point C at a depth of 100 m. Complete the outcrop of the bed. Would a sandstone bed 200 m thick appears at point D?
Determine the required depth at point D to reach the lower surface of shale.
Draw two cross sections passing through point C one is normal to the strike and the other is parallel to it. Scale 1 cm = 200 m
22
Geological maps (Dipping Beds)
hree beds outcrop- conglomerate, sandstone and shale. Complete the geological oundaries between these beds, assuming that the beds all have the same dip.
