Two geotectonic units meet within the protected areas: the Dinarides and the Pannonides. The rock here is very varied: from the ancient era (Paleozoic) to the middle era (Mesozoic) and the new era (Cenozoic).
The rock from the ancient era is between 320 and 270 million years old and can be found in the Bohor mountains (Zabukovje), Orlica (Podsreda castle), and Kunšperk. Among them are shale, quartz sandstone, quartz conglomerates, and siltstones.
However, the much stronger presence of rock from the middle era, it comprises the surface of Boč, Resevna, Voluš, Rudnica, Bohor, Oslica, Vetrnik, and Orlica. The rock is between 250 and 70 million years old. It comprises mostly sedimentary rock, such as sandstone, claystone, marls, limestone, and dolomites. In several places (Svetina, Resevna, Rudnica, Bohor, Orlica) there is igneous rock on the surface, such as diabases, keratophyre and their tuffs.
The most widespread rock in the protected area is rock from the new era. They make up the rolling hills that accommodate vineyards and orchards as well as fields along the Bistrica and Sotla rivers. Layers of this rock began depositing around 34 million years ago, and are present as marls, claystone, sandstone and conglomerates.
The park territory has a complex tectonic composition, which belongs to the Dinarides and Pannonides geotectonic units. With its numerous fault lines, it is divided into larger and smaller clumps that were pushed up or down along the faults. From north to south, the following tectonic units can be found: the Laško syncline, Rudnik anticline, Planina syncline, Litija anticline, Senovo syncline, Orlica anticline, and Bizeljsko syncline.
Larger spots within the protected area feature rich fossil deposits. They can be found in the middle era rock, however fossils can be found even more often in the rock from the new era.
On the mountains of Rudnica, Bohor and Orlica, several shell particles and snail shells have been found, whereas also remains of cephalopods have been found on Bohor. On Vetrnik and south from Kozje, remains of a megalodon seashell were found. In several samples from the wider region of the park, microfossils of a foram (foraminifera) also were found.
The most interesting is the finding of a fish from the Lates genus, found near the Slivje village on the south slope of Rudnica. Very common are the fossils of sea urchins, seashells, snails, crabs, and shark teeth. Most of sites are located in the vicinity of Podsreda, Kozje, Vojsko and Bizeljsko.[su_photo_panel shadow=”0px 1px 2px #eeeeee” photo=”http://kozjanski-park.si/wp-content/uploads/2015/04/3.3.1_geološka-karta.jpg”]Geološka karta[/su_photo_panel] [su_photo_panel shadow=”0px 1px 2px #eeeeee” photo=”http://kozjanski-park.si/wp-content/uploads/2015/04/3.3.3_geološka-obdobja-zemlje.jpg”]Geološka karta[/su_photo_panel] [su_photo_panel shadow=”0px 1px 2px #eeeeee” photo=”http://kozjanski-park.si/wp-content/uploads/2015/04/3.3.2_geološka-karta-legenda.jpg”]Legenda geološke karte[/su_photo_panel]