66
Water In Ecosystems: A Non Renewable Resource
In the Felix units, there are also two members; the lower one comprised of phyllite,
schist and quartzite; and the upper carbonate member, composed mainly of
dolomite. The age of these units IS approximately Permo-Werfenian to MiddleLate Triassic (Pulido et ai., 1993). No deposits are known between the Late
Triassic and the Miocene. The Late Miocene materials outcrop in the northern
margin of the Campo de Dalias, over limestone and dolomite and also over
phyllite and quartzite of both units. The Pliocene is represented by a lowest
conglomerate upon which a marl marine formation was deposited in varying
thicknesses of possibly more than 700 m. Calcarenites, reaching over 100 m, are at
the top of this formation. Quaternary materials are widely represented, with diverse
facies (Fourniguet, 1975): from alluvial fans to older marine Quaternary deposits.
The most important tectonic phase was the one that gave rise to the movement of
the Felix umts thrusting over the Gador ones. The deformations that contributed
mainly to the current morphology were neotectonic, involving stages of fracturing,
tilting and uI?lifting. After the Late Miocene, the swell of Gador fractured in the
dominant strIke N 70 E. Normal faults with great thrusts produced a series of
compartments within the basin; a horst and a graben appeared, occupying the
central sector of the Campo de Dalias (Pulido et ai., 1989).
In relation with the hydrogeological features of this area, three hydrogeological
units can be distinguished at the Campo de Dalias (IGME, 1982; Dominguez et ai.,
1988; Pulido, et ai., 1989) involving a complex structure to be studied (see Fig. 1):
1.1 Balerma-Las Marinas Unit
This aquifer has the greatest surface area of the Campo de Dalias, with nearly
225 km 2 of outcrop. This is essentially composed of Pliocene calcarenites, whose
thickness decreases from north to south, while the proportion of terrigenous
components increases. Balerma-Las Marinas presents a great variety of
transmissivity (IGME, 1982), showing values from 1800 m 2 /day to 120 m 2 /day.
Most farming activity is located in this aquifer unit. The whole area is below sea
level and the temporal piezometric evolution indicates a general tendency to rise
or stabilise (Thauvin, 1986). This situation is reflected in the poor natural quality
of the water (Pulido et ai., 1989). Pumping in this unit reaches 15 Hm3/year and
the total mean influx is estimated at 18-24 Hm3/year.
1.2 Balanegra Unit
This water reservoir occupies the western half of the Campo and is partly under the
Balerma-Las Marinas aquifer, being separated by Pliocene marls that act as a
confining top. The aquifer material is mainly made of dolomites from the Gador
sheet, and local Miocene calcarenites. The unit is bordered on the west and north
by the lowermost metapelites of the unit, and on the south by the sea, although the
sea is not in contact with the aquifer along the coast, but only with a slice of schist
("Escama de Balsa Nueva" slice of Balsa Nueva, Fig. 2).
Water In Ecosystems: A Non Renewable Resource
In the Felix units, there are also two members; the lower one comprised of phyllite,
schist and quartzite; and the upper carbonate member, composed mainly of
dolomite. The age of these units IS approximately Permo-Werfenian to MiddleLate Triassic (Pulido et ai., 1993). No deposits are known between the Late
Triassic and the Miocene. The Late Miocene materials outcrop in the northern
margin of the Campo de Dalias, over limestone and dolomite and also over
phyllite and quartzite of both units. The Pliocene is represented by a lowest
conglomerate upon which a marl marine formation was deposited in varying
thicknesses of possibly more than 700 m. Calcarenites, reaching over 100 m, are at
the top of this formation. Quaternary materials are widely represented, with diverse
facies (Fourniguet, 1975): from alluvial fans to older marine Quaternary deposits.
The most important tectonic phase was the one that gave rise to the movement of
the Felix umts thrusting over the Gador ones. The deformations that contributed
mainly to the current morphology were neotectonic, involving stages of fracturing,
tilting and uI?lifting. After the Late Miocene, the swell of Gador fractured in the
dominant strIke N 70 E. Normal faults with great thrusts produced a series of
compartments within the basin; a horst and a graben appeared, occupying the
central sector of the Campo de Dalias (Pulido et ai., 1989).
In relation with the hydrogeological features of this area, three hydrogeological
units can be distinguished at the Campo de Dalias (IGME, 1982; Dominguez et ai.,
1988; Pulido, et ai., 1989) involving a complex structure to be studied (see Fig. 1):
1.1 Balerma-Las Marinas Unit
This aquifer has the greatest surface area of the Campo de Dalias, with nearly
225 km 2 of outcrop. This is essentially composed of Pliocene calcarenites, whose
thickness decreases from north to south, while the proportion of terrigenous
components increases. Balerma-Las Marinas presents a great variety of
transmissivity (IGME, 1982), showing values from 1800 m 2 /day to 120 m 2 /day.
Most farming activity is located in this aquifer unit. The whole area is below sea
level and the temporal piezometric evolution indicates a general tendency to rise
or stabilise (Thauvin, 1986). This situation is reflected in the poor natural quality
of the water (Pulido et ai., 1989). Pumping in this unit reaches 15 Hm3/year and
the total mean influx is estimated at 18-24 Hm3/year.
1.2 Balanegra Unit
This water reservoir occupies the western half of the Campo and is partly under the
Balerma-Las Marinas aquifer, being separated by Pliocene marls that act as a
confining top. The aquifer material is mainly made of dolomites from the Gador
sheet, and local Miocene calcarenites. The unit is bordered on the west and north
by the lowermost metapelites of the unit, and on the south by the sea, although the
sea is not in contact with the aquifer along the coast, but only with a slice of schist
("Escama de Balsa Nueva" slice of Balsa Nueva, Fig. 2).