Formation age

Type of rocks

Thickness (m)

Main hydraulic characteristics

General consideration

Surficial recent deposits

Recent gravels, sand and silt

Up to 30 m

Local aquifer when conditions allow

Irrelevant as a source of water

Upper Cretaceous-Tertiary

Bituminous Marl

Only in small outcrops



Campanian Maastrichtian

Silicified limestone overlain by beds of phosphatic chert

Around 70 m

Excellent aquifer

Good to excellent Aquifer


Massive sandy limestone

55 m

Good aquifer


Alternating beds of limestone, dolomite, marly limestone, dolomitic limestone, sandstone, marl and some gypsum layers

Around 300 m

Poorly developed aquifer. In many areas springs issue from the limestone and dolomite beds

In general, poorly developed aquifer with some good yield aquifer layers. On a regional scale it leaks water down into the older aquifers

Lower Cretaceous

Coarse, medium and fine-grained sandstone

150 m

Good aquifer

Good to excellent aquifer directly overlying Silurian sandstones

Silurian-Cambrian sandstone series

Mainly coarse, medium and coarse-grained sandstone

1300 - 1400 m

Excellent aquifer

Excellent aquifer