4.1 Horizontal stratigraphy

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4.1 Horizontal stratigraphy In this model an East-West trending valley dissects a simple horizontal layered stratigraphy, so that the outcrop pattern follows the contours of the topography. The results are compared for a barometric survey, where the survey locations are at a constant height above sea level (in this case 400 m above the top of the block), and a draped survey, where the survey locations maintain a constant height above the local land surface (in this case 400 m above the land surface). Click on the images to launch Noddy. A legend is provided at the end of this page.


	Block model showing topography dissecting a three layer stratigraphy. LOAD JPEG IMAGE In order to use these history files you will also need to download the following file! topofile.top

	Barometric Survey	Draped Survey
Link
Gravity	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Gravity	In this image the gravity field only reflects the general shape of the topography, and the position of the high density layer is not immediately obvious.	In this image the gravity field reflects the shape of the topography, and the sharp gradient (which follows the contours) marks the position of the high-density layer.
Magnetics	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Magnetics	In this image the magnetic field only reflects the general shape of the topography, although there is a strong asymmetry between the North and South facing slopes of the valley, and the exact position of the high susceptibility layer is unclear.	In this image the magnetic field reflects the shape of the topography, and the position of the high susceptibility layer is marked by a low contour-following low on the South-facing slope, and a contour-following high on the North-facing slope.
Magnetics	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Magnetics	In this image the magnetic field only reflects the general shape of the topography, although there is a strong asymmetry between the North and South facing slopes of the valley, and the exact position of the high susceptibility layer is unclear.	In this image the magnetic field reflects the shape of the topography, and the position of the high susceptibility layer is marked by a low contour-following low on the South-facing slope, and a contour-following high on the North-facing slope.
Magnetics at Pole	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Magnetics at Pole	In this image the magnetic field only reflects the general shape of the topography, and since this image is calculated at the South Pole, the North- and South-facing slopes behave in the same way. The exact position of the high susceptibility layer is unclear.	In this image the magnetic field reflects the shape of the topography, and the position of the high susceptibility layer is marked by a sharp transition in intensity values.
Magnetics at Pole 1VD	LOAD TIFF IMAGE	LOAD TIFF IMAGE
Magnetics at Pole 1VD	In this image the magnetic field only reflects the general shape of the topography, and since this image is calculated at the South Pole, the North- and South-facing slopes behave in the same way. The exact position of the high susceptibility layer is roughly marked by the sharp transition in intensity values.	In this image the magnetic field reflects the shape of the topography, and the position of the high susceptibility layer is marked by a contour-following dipole anomaly.

Key Survey Specifications Scales

green

k = 0 r = 0

green layer

k = 1.1×10^-3

purple

k = 10^-2 r = 3

purple layer

k = 0

image width

10,000 m

inclination

50° or 90°

intensity

50,000 or 70,000 gamma

flying height

400 m

max

min

max

min

WWW conversion by Ian Brayshaw