Geology Reference
In-Depth Information
The commercial production in the depression comes from the clastic and
carbonate reservoirs. The entire penetrated section is mostly gas-saturated.
The major fields are associated with the Pliocene deposits. Small gas accu-
mulations are found in the Miocene sandstones (Cortemaggiore, Desana
and Vigarro fields), which also include small oil fields (Cortemaggiore,
Podenzano, Valenza and Salsomaggiore fields). In recent years, commer-
cial hydrocarbons were discovered in the Triassic limestones and dolo-
mites where rather large gas and condensate accumulations (about 50
BCM) have been identified. The hydrocarbon accumulations basically
form three zones: the upper gas zone, the middle oil zone and the lower
gas-condensate zone. Over 80% of the discovered reserves are shallower
than 2,000 m.
1.1.3
The Viennese Depression
The depression is a folded graben bounded on all sides by deep-seated
faults. The basin's boundaries in the north and northwest are Flysh and
Limestone Alps, in the east Small Carpathians and Heinburg Mountains,
and in the south and southeast northeastern offspurs of the Central
Alps (Rosalien and Leita Mountains) (Figure 1.5). The Lower Miocene
(Burdigalian, Helvetian) through the Pliocene-Quaternary interval of the
basin comprises mostly sandy-silty deposits up to 6 km thick. In the north-
western region, this sequence overlies the eroded surface of the Cretaceous-
Paleogene flysh and in the southwest it overlies intensely deformed Jurassic
and Triassic carbonates of the Ötscher, Luntz and Frankenfels nappes.
In
the southeast, the Neogene is underlain by Paleozoic metamorphic rocks.
The average total sediment cover thickness is 9.5 km; the clay content is
close to 50%.
A clear pattern is observed in the Neogene facies and thicknesses. The
central areas of the basin with maximum thicknesses are composed by
clays and marl rocks. The border areas are dominated by sandstone and
conglomerate series.
The section of the region is subdivided into two structure-
lithostratigraphic stages. The lower one includes mostly carbonates and
metamorphic rocks of the pre-Neogene series. The upper one is composed
by Neogene (Pliocene and Miocene) clastics. The major lineaments in
the region are large regional normal faults (the Steinberg, Leopoldsdorf,
Aderclaa and Lab-Shashtin). The amount of throw on these faults reaches
1,000 to 1,500 m, sometimes 2,000 m. The cross-faults (Mühlberg,
Zisterdorf, Danube, etc.)
cause step-block descending of the Alpine basal
complex.
