How is a geological map made?
To make a geological map, there are a series of steps:
Planification
- Search of publications or public documents about previous geological works carried out in the zone to cover with the geological cartography to carry out.
- Study of the characteristics of the relief of the zone to map: geological photointerpretation.
Field work
The geologist makes a serie of itineraries for the field searching rocks outcrops
When it finds an outcrop, he places it on the topographic map or on the air photo. Some glasses called stereoscopes allow him to see the photos aerial in relief.
With a hammer and a magnifying glass, he identifies the rock and he searches fossils, which often have millimetric size.
With a compass of geologist, with clinometer and level, he measures the dip of the strata, the schistosity, the faults, the lineations, etc.
In a field notebook, he aims the number of station and, next, all the observed and moderate data (dip, lithology, fossils, samples, etc). Often he makes outlines of the geometry of the layers.
Cabinet work
With the knowledge of the data of the subsoil and the data of the geology of area acquired with the fieldwork, the geologist deduces the structure from the materials many meters under the area of the surface terrain.
About the topographic map it places a transparent polyester, where he places the stations observed in the field. In every station the dip of the shapes and other observations are indicated.
He places the limits among the observed rocky units. He interpolates them and he plots the lines of contacts. If the dip of the layers is next to the horizontal, the contacts are very sinuous (like the contour curves), however, if it is next to the handstand the contacts will be straight lines.
For interpreting the map, the geologist carries out a series of geological cross sections, perpendicular to the structures.
These cross sections can show a series of problems which the geologist can not solve with the data that he has. Then it is necessary to come back to zones in the field where he had not been yet to obtain more data, or to come back to the same places in order to complete or correct the interpretation. In this way, it starts a cycle that finishes when the geologist considers that the map has the suitable quality.
Consultation and interpretation of the disposable subsoil data:
- Seismic profiles
- Wells of hydrocarbons exploration
- Water surveys
Laboratory data: area samples
- Paleontological datings
- Radiometric datings
- Geochemistry analysis
- Petrologics studies
- Paleo-environmental studies
Publication
Geological maps can be downloaded in GeoPDF format with geospatial capabilities from the Geological geoinformation catalog and/or acquired in paper format from the online store.