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Attitude of beds

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Pramod Hanamgond
Pramod Hanamgond

1. Strike is the direction of the intersection of a geologic structure with a horizontal plane, while dip is the angle of inclination from horizontal. 2. A Brunton compass is used to measure the strike and dip of geologic structures in the field. 3. An outcrop is an exposure of a rock formation at the surface, and its pattern depends on factors like the structure's orientation and the topography.

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Attitude of beds, Strike and dip, Brunton compass and its use; and Outcrops Dr. P. T. Hanamgond GSS College, Belgaum
Describing and mapping the orientation of a geologic structure such as a inclined sedimentary bed, a fault plane, a joint plane etc involves determining … Strike (trend) Dip (inclination) Hence, attitude of a bed is defined as the strike and dip of a bed. Mapping Geologic Structures in the field
Strike (trend) The direction of the line produced by the intersection of an inclined rock layer or fault or a dyke or a mineral vein with a horizontal plane. Generally expressed as an angle relative to north. N37°E – S37°W N12°W – S12°E Fracture Ripple Structure Dyke Fault
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Dip (inclination) The angle of inclination of the surface of a rock unit or fault measured from a horizontal plane. Includes both an angle of inclination and a direction toward which the rock is inc lined. For Ex., 82°SE 17°SW Dip values always are in the range 0-90° . A dip angle of 0° defines a horizontal attitude. 90° of dip describes a vertically oriented plane. 0-20°: Shallow 20-50°: Moderate 50-90°: Steep Direction of dip
In case of horizontal beds, sedimentary beds are originally deposited as a series of horizontal layers one on top of another,.. Conformably Imaginary horizontal plane
The principle of superposition states that, in a series of undisturbed layers, the oldest layer is on the bottom and each overlying layer is progressively younger with the youngest layer on the top. When the outcrop lines are parallel the beds are conformable and have the same amount of dip.
When there are two outcrops with sudden change in strike and dip, it indicates that the beds are unconformable. Unconformable Younger Older
True dip – It is the shortest distance of the dip of a bed or rock formation or it is the maximum dip or slope of a bed with respect to the horizon. In the diagram - SS represents the strike direction and ‘ad’ is the dip direction. S A B C E D O S d S Sa Apparent dip – in the given figure SS represents the strike direction and OD is the true dip direction which is perpendicular to the strike. The other dip directions such as OA, OB, OC, OE are all called the apparent dips. In other words, the directions of dip other than the direction of true dip (OD) are described as apparent dips. They are less than 90°. Types of dip
Beside true dip and apparent dip the dip is also differentiated in following ways. Primary or Initial dip – It is the inclination of strata due to the original slope of a basin. These dips are generally less than 35° (generally 0° – 20°). Secondary dip – It is the inclination induced in the strata after its deposition due to the tectonic forces to which the strata is subjected. These dips may be from 0° – 90°. Local or Regional dip – It is the inclination of rocks exposed in a limited area of observation.
Attitude of beds
Geologists use a Brunton or Clino compass to measure strike and dip. When using the compass to determine the attitude of a plane the edge of the compass is placed against the inclined surface and then the bulls- eye bubble is centered. In this configuration the compass lies in a horizontal plane and its edge is parallel to the line produced by the intersection of the imaginary horizontal plane and the inclined surface or layer. The sighting armature points in the direction that this line is oriented, and this direction is read directly from the compass. GPS
Attitude of beds
Attitude of beds
Holding a brunton compass
Use of Brunton Compass 1. Locate North, Set local declination 2. Measure Bearings 3. Measure Strike and Dip of planes 4. Measure Trend and Plunge of lines 5. Measure Vertical Angles- measuring height / thickness of a feature
Attitude of beds
Attitude of beds
Attitude of beds
Attitude of beds
Attitude of beds
Attitude of beds
Attitude of beds
Attitude of beds
OUTCROPS
An outcrop is an exposure of a rock formation or a bed on the surface of the earth. When the outcrop lines or trend of the beds are parallel to the contour lines, the beds are horizontal.
When the outcrop lines or trend intersect the contour lines the beds are dipping or inclined. When the outcrop lines are straight and intersect the contour lines the beds are vertical.
Horizontal beds Inclined beds Vertical beds Conformable beds Unconformable beds
Attitude of beds
Inlier D C B A D C B A D A B C Younger Older Outlier Inlier – It is an outcrop of older rock surrounded by the outcrops of younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited exposure of the older underlying rocks. These are thus reverse of outliers. Valley formation is a common process of erosion, giving rise to inliers. Outlier – It is an exposure of a younger bed surrounded by the outcrops of older formation. It results due to excessive erosion or due to faulting followed by erosion. C D B C D E E B A C D E B A Inlier Outlier TYPES OF OUTCROP There are two types of outcrop created because of selective erosion of rocks in certain areas known as Outlier and Inlier. These are well exposed in a folded regions.
OUTCROP PATTERN The outcrop of the top or bottom of horizontal bed follows topographic contours. The width of the outcrop of a horizontal bed depends upon the thickness of the bed and upon the topography. Strata may be horizontal, inclined or vertical. The thickness is measured perpendicular to the bedding plane. Exposed bed Earth Surface The outcrop pattern of a tilted bed depends on the angle of tilt and on the surface topography.
The width of the outcrop depends upon the tilt and slope of the ground. When the bed is vertical the width of the outcrop is minimum or it is equal to the true thickness of the bed. If the ground surface is flat, but the bedding angle is change then also the width of the outcrop varies. Similarly the change in slope of the ground also matters. The higher the slope of the ground wider the outcrop. A C B Thickness of beds A, B and C is the same but outcrop of B is much wider than A and outcrop of C is much wider than B, due to their shallower dip angle
When the outcrop runs in the strike direction it tends to keep an approximately even width. If the inclination of the ground is towards the dip direction the width of the outcrop is maximum. t d d t When the dip is 0° (horizontal beds), the width of the outcrop becomes infinity, i.e., the outcrop will occupy the whole of the ground surface. Horizontal surface- width is minimum Inclination of ground towards the dip – width is maximum
A B Figure 2 C d 𝜽 ω G D Tt B A Vt Figure 1 WIDTH OF THE OUTCROP (Figure 1): AB or ω is the width of the outcrop. On the map it is the distance between the boundary of the upper surface of the bed and boundary of the lower surface of the same bed measured in right angles with the direction of the strike. THICKNESS OF THE OUTCROP (Figure 1 and 2): When the rock formation outcrops at surface of the ground, the distance between the two surfaces of the outcrop (top and bottom of the bed) is called the width of the outcrop represented by AB or ω in the figure 1. The distance GC between the top surface of the bed measured in vertical direction from the ground is called its vertical thickness (in figure 1, it is ‘d’). The distance CD measured along the direction perpendicular to the surface of the bed is its true thickness (Tt). Similarly, in figure 2, the true thickness can be measured at two levels A and B for upper surface of the bed and lower surface of the bed respectively.
DIP DIRECTION (Figure 3): Suppose a dyke/vein/a particular bed, is exposed on the surface and shows only the width, then to know which side the bed is dipping, we need to drill minimum two points at different distances on either side of the bed( G1, G2, G1’, G2’). Then if we encounter the surface of the bed at the two drilled points, measure the two levels (d1 and d2) and the direction in which the level is higher the bed will be dipping in that direction. G1 C1 C2 d2 G2 d1 Figure 3 G2” G1’
RELATION OF TOPOGRAPHY WITH RESPECT TO OUTCROP & FACTORS CONTROLLING THE WIDTH OF THE OUTCROP When the topography is horizontal and the formations are also horizontal the top most formation is continuously exposed on the surface. In an area with uneven topography the boundaries of the outcrop of a horizontal formation follows the topographic contours, whenever such horizontal formation crosses the valleys their outcrop pattern becomes U or V shaped.
If the rocks are horizontal or just slightly tilted, the outcrop follows the contours of the land
rocks tilted and eroded to a flat landscape horizontal rocks outcropping in a terraced mountain

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Attitude of beds

  • 1. Attitude of beds, Strike and dip, Brunton compass and its use; and Outcrops Dr. P. T. Hanamgond GSS College, Belgaum
  • 2. Describing and mapping the orientation of a geologic structure such as a inclined sedimentary bed, a fault plane, a joint plane etc involves determining … Strike (trend) Dip (inclination) Hence, attitude of a bed is defined as the strike and dip of a bed. Mapping Geologic Structures in the field
  • 3. Strike (trend) The direction of the line produced by the intersection of an inclined rock layer or fault or a dyke or a mineral vein with a horizontal plane. Generally expressed as an angle relative to north. N37°E – S37°W N12°W – S12°E Fracture Ripple Structure Dyke Fault
  • 5. Dip (inclination) The angle of inclination of the surface of a rock unit or fault measured from a horizontal plane. Includes both an angle of inclination and a direction toward which the rock is inc lined. For Ex., 82°SE 17°SW Dip values always are in the range 0-90° . A dip angle of 0° defines a horizontal attitude. 90° of dip describes a vertically oriented plane. 0-20°: Shallow 20-50°: Moderate 50-90°: Steep Direction of dip
  • 6. In case of horizontal beds, sedimentary beds are originally deposited as a series of horizontal layers one on top of another,.. Conformably Imaginary horizontal plane
  • 7. The principle of superposition states that, in a series of undisturbed layers, the oldest layer is on the bottom and each overlying layer is progressively younger with the youngest layer on the top. When the outcrop lines are parallel the beds are conformable and have the same amount of dip.
  • 8. When there are two outcrops with sudden change in strike and dip, it indicates that the beds are unconformable. Unconformable Younger Older
  • 9. True dip – It is the shortest distance of the dip of a bed or rock formation or it is the maximum dip or slope of a bed with respect to the horizon. In the diagram - SS represents the strike direction and ‘ad’ is the dip direction. S A B C E D O S d S Sa Apparent dip – in the given figure SS represents the strike direction and OD is the true dip direction which is perpendicular to the strike. The other dip directions such as OA, OB, OC, OE are all called the apparent dips. In other words, the directions of dip other than the direction of true dip (OD) are described as apparent dips. They are less than 90°. Types of dip
  • 10. Beside true dip and apparent dip the dip is also differentiated in following ways. Primary or Initial dip – It is the inclination of strata due to the original slope of a basin. These dips are generally less than 35° (generally 0° – 20°). Secondary dip – It is the inclination induced in the strata after its deposition due to the tectonic forces to which the strata is subjected. These dips may be from 0° – 90°. Local or Regional dip – It is the inclination of rocks exposed in a limited area of observation.
  • 12. Geologists use a Brunton or Clino compass to measure strike and dip. When using the compass to determine the attitude of a plane the edge of the compass is placed against the inclined surface and then the bulls- eye bubble is centered. In this configuration the compass lies in a horizontal plane and its edge is parallel to the line produced by the intersection of the imaginary horizontal plane and the inclined surface or layer. The sighting armature points in the direction that this line is oriented, and this direction is read directly from the compass. GPS
  • 15. Holding a brunton compass
  • 16. Use of Brunton Compass 1. Locate North, Set local declination 2. Measure Bearings 3. Measure Strike and Dip of planes 4. Measure Trend and Plunge of lines 5. Measure Vertical Angles- measuring height / thickness of a feature
  • 26. An outcrop is an exposure of a rock formation or a bed on the surface of the earth. When the outcrop lines or trend of the beds are parallel to the contour lines, the beds are horizontal.
  • 27. When the outcrop lines or trend intersect the contour lines the beds are dipping or inclined. When the outcrop lines are straight and intersect the contour lines the beds are vertical.
  • 30. Inlier D C B A D C B A D A B C Younger Older Outlier Inlier – It is an outcrop of older rock surrounded by the outcrops of younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited exposure of the older underlying rocks. These are thus reverse of outliers. Valley formation is a common process of erosion, giving rise to inliers. Outlier – It is an exposure of a younger bed surrounded by the outcrops of older formation. It results due to excessive erosion or due to faulting followed by erosion. C D B C D E E B A C D E B A Inlier Outlier TYPES OF OUTCROP There are two types of outcrop created because of selective erosion of rocks in certain areas known as Outlier and Inlier. These are well exposed in a folded regions.
  • 31. OUTCROP PATTERN The outcrop of the top or bottom of horizontal bed follows topographic contours. The width of the outcrop of a horizontal bed depends upon the thickness of the bed and upon the topography. Strata may be horizontal, inclined or vertical. The thickness is measured perpendicular to the bedding plane. Exposed bed Earth Surface The outcrop pattern of a tilted bed depends on the angle of tilt and on the surface topography.
  • 32. The width of the outcrop depends upon the tilt and slope of the ground. When the bed is vertical the width of the outcrop is minimum or it is equal to the true thickness of the bed. If the ground surface is flat, but the bedding angle is change then also the width of the outcrop varies. Similarly the change in slope of the ground also matters. The higher the slope of the ground wider the outcrop. A C B Thickness of beds A, B and C is the same but outcrop of B is much wider than A and outcrop of C is much wider than B, due to their shallower dip angle
  • 33. When the outcrop runs in the strike direction it tends to keep an approximately even width. If the inclination of the ground is towards the dip direction the width of the outcrop is maximum. t d d t When the dip is 0° (horizontal beds), the width of the outcrop becomes infinity, i.e., the outcrop will occupy the whole of the ground surface. Horizontal surface- width is minimum Inclination of ground towards the dip – width is maximum
  • 34. A B Figure 2 C d 𝜽 ω G D Tt B A Vt Figure 1 WIDTH OF THE OUTCROP (Figure 1): AB or ω is the width of the outcrop. On the map it is the distance between the boundary of the upper surface of the bed and boundary of the lower surface of the same bed measured in right angles with the direction of the strike. THICKNESS OF THE OUTCROP (Figure 1 and 2): When the rock formation outcrops at surface of the ground, the distance between the two surfaces of the outcrop (top and bottom of the bed) is called the width of the outcrop represented by AB or ω in the figure 1. The distance GC between the top surface of the bed measured in vertical direction from the ground is called its vertical thickness (in figure 1, it is ‘d’). The distance CD measured along the direction perpendicular to the surface of the bed is its true thickness (Tt). Similarly, in figure 2, the true thickness can be measured at two levels A and B for upper surface of the bed and lower surface of the bed respectively.
  • 35. DIP DIRECTION (Figure 3): Suppose a dyke/vein/a particular bed, is exposed on the surface and shows only the width, then to know which side the bed is dipping, we need to drill minimum two points at different distances on either side of the bed( G1, G2, G1’, G2’). Then if we encounter the surface of the bed at the two drilled points, measure the two levels (d1 and d2) and the direction in which the level is higher the bed will be dipping in that direction. G1 C1 C2 d2 G2 d1 Figure 3 G2” G1’
  • 36. RELATION OF TOPOGRAPHY WITH RESPECT TO OUTCROP & FACTORS CONTROLLING THE WIDTH OF THE OUTCROP When the topography is horizontal and the formations are also horizontal the top most formation is continuously exposed on the surface. In an area with uneven topography the boundaries of the outcrop of a horizontal formation follows the topographic contours, whenever such horizontal formation crosses the valleys their outcrop pattern becomes U or V shaped.
  • 37. If the rocks are horizontal or just slightly tilted, the outcrop follows the contours of the land
  • 38. rocks tilted and eroded to a flat landscape horizontal rocks outcropping in a terraced mountain