Offshore bedrock 250K

The 1:250 000-scale offshore geological maps are available digitally as two themes: offshore bedrock geology and seabed sediments.

The overlying column of sea water imposes major limitations offshore that make it impossible to use normal, onshore, geological mapping techniques. However, other techniques, such as ship-board geophysical surveys, can be used that allow geological interpretations using evidence not normally available onshore.

The offshore bedrock geology theme is essentially the same as that mapped onshore, but it is usually much less detailed. Onshore, a lithostratigraphical nomenclature is used with rocks routinely mapped at formation, member and bed level. Offshore, this is often impossible and rocks are commonly referred to by age. Where it is possible, mapping is usually only to group or formation level at best and even these may not be differentiated into individual units, but shown only as part of a package of units.