The Infiltration of Water Below Ground and the Concept of an Aquifer - Hydrogeology: Objectives, Methods, Applications - page 35

Lithology therefore plays an important role in hydrogeologic features:
aquifers within which water circulates due to gravity, thanks to large-scale
solid elements (gravel, sand, sandstone), aquitards containing water with
low mobility (silt, clayey sand), aquicludes containing water that is slow
to renew (clay, marl).
Structure plays a major role in determining the drainage and
communication potential across aquifers. Sedimentary structures (channels
and gravel bodies within clays) in detrital continental formations, tectonic
structures, and faults allow both the drainage of coherent formations
(sandstone, limestone, granite, gneiss, basalt) along the fault, but also
hydraulic communication between compartments, sometimes reaching
across different aquifers.
Bedding dip determines the geometry of confined aquifers: in
sedimentary basins, the alternation of water-bearing and impermeable
layers creates a multi-layered aquifer, the drainage of which may be
interrupted by brittle tectonics.
Structural geology allows for the identification of water “traps”:
monoclines terminating against impermeable layers due to a fault, synclinal
axes, grabens; and therefore, for the understanding of the geometry of
aquifers. These structures can also be better understood with geophysical
surveys.
3 DIFFERENT TYPES OF AQUIFERS (POROUS,
FRACTURED, KARST)
One can classify different types of aquifers according to the nature,
and therefore the origin, of the spaces containing water: if the voids are
intergranular spaces of sedimentary (pores sensu stricto ) or diagenetic (open
spaces left by dissolved crystals) origin, they make up intergranular porosity
or true porosity. These aquifers are called porous aquifers. They are made up
of blocks, pebbles, gravel, sand, silt, sandstone, chalk, biolithics, bioclastic
carbonates, volcanic scorias, sandy granite regolith, etc.
These aquifers are, among other things, deltaic, fl uvial, or lacustrine
alluvia, fl uvio-glacial cones, colluvia, scree, weathered mantles, scoria cones,
as well as porous marine series (detrital, bioclastic, or originating from
coral reefs). These aquifers can therefore be made up of unconsolidated
formations (often heterogeneous continental formations) or of coherent
cemented layers.
Series deposited before the Quaternary have generally undergone
diagenesis and been transformed into coherent rock.