In its two hundred years of history the geology of Park Maksimir
has not been significantly explored, especially not as a whole
of its one. However, there are some data collected by researching
surrounding geological structures, for example exploration of
Medvednica or Sava depression. Park Maksimir is located on the
contact of these two structures, on southern slopes of Medvednica
where it traverses into Sava depression.
Only two subjects out of some of significances that might
help in discovering more about geology of this area are visible
on the surface. Those are Plio-Quaternary sediment
and Holocene deposition. With their help we can determine surface's
time of origin, as well as where did that material come from.
The majority of the Park is covered with Plio-Quaternary sediment.
Geologically speaking, this sediment is rather young. Its age
is around 1.8 million years. It is interesting that it reached
Maksimir from Medvednica. In fact, from the slopes of Medvednica
various parts of rocks were brought and deposited in lakes
and marshes, which used to be in this area. This material formed
freshwater deposits that today cover the majority of Park Maksimir.
Other part of deposits, Holocene deposition, was formed in
the last 10 000 years. From the elevated parts of terrain different
streams and currents washed down the material. These rock fragments
and conglomerates deposited by water made a thin layer, which
covers the lowest part of the Park.
Lithologically speaking, both subjects have a similar composition.
This is mostly unsorted gravel, large and medium granulated
sands, silts and clay. There is not much layering, so that
they mostly form mixed sediments. Original rocks of these sediments
are green shiest, hornstone, crystal limestone, quartz, sandstone
and some ingénues rocks. Their composition additionally confirms
the fact that the surface may indeed origin from old Paleozoic
rocks from the slopes of Medvednica.
Layers of described sediments are 100- 150 m thick, and their
most interesting feature is that they are not water permeable.
In their composition they have clay and silt, which are the
most responsible for water impermeability. That is the reason
why artificial lakes in Maksimir last.
Although Park Maksimir is a small area, tectonically it is
very interesting. Three faulting lines spread in it. Two faults
spread from east to the west side. Their direction of spreading
is north to south, transversal to Medvednica ridge. The third
fault is important because it is still active. This is the,
so-called, Ilica fault, which spreads from Podsused to Zelina,
and even further. It passes the south side of the Park. During
the last 2 million years vertical shift of this fault is 20-
40 m, while today the Park is elevating with the speed of 1-
2 mm a year.