Abstract: A new method for offshore geological map compilation is introduced in this paper. For offshore mapping, the key problem is how to map the covered geological objects on geological maps. We proposed a method characterized by the combination of superposition and transparency. Superposition means that the map must be able to show the normal stratigraphic sequences, and the transparency means that it must be able to project the buried strata, igneous and other geological bodies covered by the Neogene on to the map. There are three ways to project the covered geological phenomena onto the map, namely, block, line and surface. According to the principles of transparency, the covered Mesozoic sedimentary strata, shallow basalt or acid intrusions and/or Precambrian rocks are shown on geological maps as blokes, while the boundaries of the Paleogene strata overlapping on these blocks are shown as lines. Lastly, the Neogene are shown on maps as surface and this surface is "transparent". One can see the older geological objects mentioned above through it.
The method evidently has advantage to map the superimposed geological bodies in such offshore areas as the South China Sea. It is expected to be used by other mapping programs.