GEOLOGY

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.