Geology Reference
In-Depth Information
low primary alkalinity factor values in the hydrocarbonate-
sodium medium.
t
The contrasting of positive hydrochemical anomalies (scale
of local manifestation of elevated salinity waters) in the
Neogene Stage's water complexes directly depends on the
extent of structures' faulting. The strongest faulted struc-
tures include maximum amounts of high-salinity formation
waters.
It is noteworthy that the aforementioned increase in ground water
salinity and hardness (decrease in alkalinity in a hydrocarbonate-sodium
medium) with stratigraphic depth is not always smooth and consistent.
In some cases (for instance at Matzen and Schonkirchen, in the upper
section (Pannonian, Sarmatian Stages) the salinity increases with depth
accompanied by decreasing primary alkalinity factor. In the underly-
ing Tortonian Stageе it declines (with increase in alkalinity: Koelbl, 1958;
Schrocfcenfuchs, 1975). In the Helvetian and Burdigalian Stages it grows
again (Figure 2.26). The inversion nature of hydrochemical zoning in the
Middle Miocene interval of the stated fields is most likely associated with
dehydration of clay members in the complex. Under the environment of
elevated temperature, it results in the release of carbonate-enriched low-
salinity waters subsequently mixing with depositional alkalineми higher
salinity waters of the hydrochemical background. Some scientists believe
that this phenomenon is caused by cross-flow of lower salinity waters from
the overlying beds (Kapounek, Koelbl and Weinberger, 1963). This view
does not appear convincing due to the presence in the Tortonian Stage
of
a positive (Boldizar,
1968) rather than negative geotemperature anomaly
that should have appeared if colder waters percolated from above. The
other possible factors could be limited reservoir injectivity and fault con-
ductivity within Tortonian complex. Those actions could have restricted
the injection into its section of lower chlorine-calcium brines (see further),
thereby providing for the preservation in a relatively little changed form of
the hydrochemical background alkaline waters. In the upper stratigraphic
intervals, these parameters have higher values and the invasion of lower
waters may have been more intense. That would create seeming salinity
decrease down the section.
Ground water distribution in the section and over the area of local
structures provides an opportunity to estimate the role of various geologic
factors and mechanisms in the formation of their component composition
and salinity. It also allows establishing the extent to which the actual chem-
istry of the water medium fits different theoretical models.
