Geology Reference
In-Depth Information
Ground waters from the
Upper Cretaceous
fractured limestones and
dolomites were produced in the Cortemaggiore Field. Its component
composition is of the chlorine-calcium type; the salinity is 390.5-408.6
mg.-equiv. (111.6-116.7 g/l); the secondary salinity factor is 25.14-
27.12%-equiv., sulphate-ion concentration is 5.01-5.97 mg.-equiv. (depth
5,250 m).
he
Oligocene-Lower Miocene
complex is composed of sandstones, con-
glomerates and clays saturated with waters of the hydrocarbonate-sodium
type with salinity 75.3-83.5 mg.-equiv. (21.5-23.9 g/l) and primary alka-
linity factor 6.49-10.15%-equiv. (Salsomaggiore and Caviaga fields).
he
Middle-Upper Miocene
clastic complex is also saturated with alka-
line relatively low-salinity (57.2-65.4 mg.-equiv. or 16.3-18.7 g/l) waters
with the primary alkalinity factor of 15.08-18.22%-equiv. (Cortemaggiore,
Santerno and
Podenzano fields).
A distinctive feature for the interval's
waters
is elevated sulphate content (up to 4.0 mg.-equiv.). This is associated
with gypsum and anhydrite interbeds in the upper portion of the com-
plex (Sarmatian Stage) (Bakirov, Varentsov and Bakirov, 1970; Reference
book…, 1976).
The hydrochemical background of the
Pliocene
complex (a nonuniform
clay-sandstone sequence with lenses and common pinch-outs of the res-
ervoir members) is formed by hydrocarbonate-sodium waters with salin-
ity 42.6
−
51.8 mg.-equiv. (12.2
−
14.8 g/l) and the primary alkalinity factor
20.16
25.63%-equiv. (Alfonsine, Ravenna, Ravenna-Mare, Cortemaggiore
and Porto-Corsine-Mare fields).
he
Pleistocene
complex comprises coarse-grained basal sandstones,
sands, clays and marls saturated with low-salinity (30
−
−
35 mg.-equiv. or
8.6
−
10 g/l) high-alkaline waters with primary alkalinity factor 27.60
−
31.14%-equiv. (Corregio, Ravenna and Bordolano fields).
A specific hydrochemical feature in the region's ground waters is a con-
tinuous growth, beginning with depth of around 1,500
1,600 m, in the sul-
phate-ion content with depth. The correlation “SO
2
−
vs. depth” is described
by the equation SO
2
−
= 0.24
−
Н
1.988
, and “SO
2
−
vs. temperature”, SO
2
−
=
⋅
10
6
⋅
2.18
t
3.059
(Figures 2.22, 2.23).
The sulphates in waters of clastic Neogene complexes appear to be
mostly a result of the thermochemical filtration leaching of the enclos-
ing rocks under the Kissin and Pakhomov (1970), Kononov (1965) and
Krasintseva (1968) model (Vadas, 1964) and of the injection of lower, SO
2
−
-
enriched waters. In the Upper Miocene interval where gypsum and anhy-
drite interbeds are common, these processes are additionally superposed
by the effects of their dissolution. In the Mesozoic sediments the water
enrichment in the sulphate-ion occurs mostly due to the dissolution of the
⋅
10
-6
⋅
