Karst Aquifers - Hydrogeology: Objectives, Methods, Applications - page 58

Figure 31 Schematic cross-section of the Fontaine de Vaucluse.
More recent explorations show that the conduit is complex, and cannot
be simplifi ed to a simple gallery. The volume becomes greater and greater
with increasing depth, giving the impression of a vast, bell-shaped sinkhole.
Its exact shape remains undefi ned, and the rest of the cavity is unknown.
Two small galleries at 40 and 50 m a.s.l. feed perennial springs.
4.1.2 Geology
The fountain is hollowed out of Urgonian (Barremo-Aptian) limestones.
These are between 500 and 800 m thick, and are part of a limestone series
approximately 1500 m thick. The general structure is a monoclinal block
dipping south, and cut across by a network of north-south faults (N 30°
and N 145°). To the west the karst is barred by the Cavaillon/Fontaine-de-
Vaucluse fault, which puts the Cenozoic series of the Plaine du Comtat and
Carpentras basin into contact with the Urgonian limestones. To the south,
they sink beneath the marly syncline of the Apt basin. Farther south still,
the marly core of the Lubéron anticline forms a hydrogeologic barrier. To
the extreme east, the Durance fault system bars the karst. The impermeable
substratum is composed of Neocomian marl.