Geological Mapping

This page gives some theory background for the unit standard on geological mapping

What is a geological map

A geological map shows the rocks that you would see at the surface, if all the vegetation and man-made features and soil were stripped away. The rocks are usually grouped into units called formation, which are the basic geological units (like a species in biology). A formation is a group of related rocks which share some characteristics, most usually
  • the rock type (igneous, sedimentary, sandstone, etc.) - but there may be more than one type of rock in a formation
  • the time period at which the rocks were formed (usually an interval of time e.g. upper Palaeocene to Lower Miocene)
  • the rocks are usually coeval, sharing either a mechanism of formation or environment of formation. This is often the most critical part of the definition, as a single event or environment can produce a range of rock types which are related e.g. a volcanic eruption may produce a formation called a tephra, but it msy differ significantly from the near-vent (proximal) to the further away (distal) deposits.
In practice, geologists tend to map units of rock which are recognizable over a distance.