Geology of Croatia

Precambrian rocks only outcrop in the north in between the Sava River and Drava River and include amphibolite schist, micaschist, gneiss and granites. Early Paleozoic rocks include clastic rocks with calcareous intercalations near the Pannonian region and along the Inner Hinterland. Only Ordovician, Silurian and Devonian rocks have been confirmed with fossil evidence. Conglomerate, shale and sandstone are typical of the late Paleozoic. Inliers and overthrusts from this period (Carboniferous-Permian) are up to 3.5 kilometers thick in the Main Dinaric Ridge.

A gap in sedimentation defines the boundary between the Permian and beginning of the Mesozoic in the Triassic. Allochthon dolomite and clastic rocks are common. Early Triassic rocks include siltite, mica, shale, thin limestone, gypsum and dolomite, while shelf limestone, dolomite and ammonite nests are typical of the Middle Triassic. Platy limestone, tuff and andesite from igneous activity are also common in this time frame.

Up to 2.5 kilometers of reef limestone deposited in the Dinaric and Adriatic areas in the Jurassic and Malmian pelagic chert outcrops in the Main Dinaric Ridge. Oceanic rock appears in the Dogger-Malm time with green sandstone, peridotite, serpentinite, spilite, diabase and melaphyre. Platy limestone and chert deposited widely, up to four kilometers thick in the Cretaceous.

Cenozoic Paleogene rocks unconformably overlie Cretaceous rocks with bauxite, coal and freshwater limestone, overlain by marine limestone from the Eocene and flysch formed in a trough between two carbonate platforms. Sandstone, marl and limestone deposited in basins now beneath the Adriatic Sea during the Neogene. In the Pannonian area, Neogene material lies on top of older bedrock, emplaced on the periphery of the Paratethys Ocean. Neogene rocks include marl, conglomerate, sandstone, as well as andesite and tuff. In the Drava River valley, the Neogene is seven kilometers thick. Many units contain lignit and oil is found in lower units. Sand and clay from the last 2.5 million years of the Quaternary unconformably overlies Neogene rocks beneath the Adriatic. Karst rivers often contain glacial sediments and terra rossa is common both offshore and on the Main Dinaric Ridge. [2]

Croatia is part of the Dinarides. Early tectonic evolution in the Precambrian or Paleozoic is difficult to determine due to reworking in subsequent orogenies. The region's carbonate platform was split by an open sea belt in the Triassic, creating the Adriatic and Dinaric platforms. It resulted in local, intense continental subduction. Ultramafic ophiolite formed with the opening of a branch of the Tethys Ocean in the Cretaceous, followed by magmatic activity. With continued continental subduction in the Paleogene, uplift and the formation of tectonic windows began. The Adriaticum is a carbonate platform structural belt with Mesozoic-Paleogene flysch, chert and limestone superimposed on it. The Supradinaricum forms a nappe on the Dinaricum and are tectonically complex with oceanic rocks underlain by platform deposits.

Evidence of the Carboniferous Variscan orogeny remains in Mt. Papuk in the east. [3]

Coal, oil, gas and water are the leading natural resources in Croatia. The carbonate platform karst landscape of Croatia helped to create the weathering conditions to form bauxite. Anhydrite, gypsum, clay, sand amphibolite, granite, spilite, gabbro, diabase and limestone are all quarried for building. [3]