Transcript Peta geologi - Universiti Sains Malaysia

Peta geologi
• What is a geological map ?
• A geological map gives information on the
superficial layers of the earth’s crust. The
geological formations are listed according to
their composition (lithology), their age
(stratigraphy) and their structural position
(tectonic). They are placed on a topographic
base (map) using different graphic elements
(symbols, figuratives and colors). The choice of
scale depends on the geological content and the
intended objective of the map.
• A geologic map is an illustration of a huge
volume of geologic information. Using a
geological map, a geologist can show the
distribution of rock bodies at the surface
of the Earth and geologic structures
which have deformed those rocks. [Photo
of Bright Angel quadrangle}
• Geological maps show the occurrence,
nature, extent and stratigraphic age of
rock strata in a district
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How are geological maps made ?
The essential condition for establishing a geological detail map is a precise
field survey, based on numerous measurements and observations. The
topographic base is generally taken from maps at a scale of 1:10'000, such
as those of the comprehensive cadastral plans.
The field geologist determines the rock type according to various criteria
and measures its orientation. All data are transcribed onto the map and in a
field notebook. Besides the natural or artificial outcrops, data from bore
holes or important test holes are taken in consideration.
In the case of a doubtful rock identification, complementary investigations
are carried out in the laboratory on samples of these rocks.
At the end of the field survey, the geologist establishes an original draft at a
scale of 1:25'000 and constructs some geological sections across the
studied sector. He also writes an explanatory note that generally contains
numerous illustrations.
The geological cartography section assures the direction of the project,
carries out the editing of the map, establishes the final legend of the map
and provides indispensable data for the cartographers.
Bright Angle Quadrangle