A journey that lasted millions of years
Limestone, and partly dolomite rocks, were formed in a shallow in a process of sedimentation and cementation of carbonic mire and skeletons of living organisms through vaste eons of geological past.
The area where some of the hugest limestone rock masses of today's karst were shaped is called the Adriatic carbonic platform. It nowadays belongs to the group of fossil platforms, because it ceased to exist some 40 million years ago.
This area consisted of the vaste, shallow sea, rimmed by deep ocean spaces. On the edges of this platform, exuberant life was developed, floral and faunal; and in the very middle, protected from strong sea currents and waves, ruled miled conditions in which most of the limestone masses originated.
The sea bottom was of a rough relief, with many ledges, cliffs, barrows and small valleys. Influenced by tides and tectonic movements, some parts of the terrain often rose above the sea surface and emerged as islands.
In the beggining of formation, the carbonic platform was placed between the 10th and the 15th degree of northern latitude, and before its end it resided between the 30th and the 35th degree of northern latitude. Today's remnants of that platform, our karst area, are positioned between the 42nd and the 46th parallel.
The speed of movement increased during Mesosoic, and it reaches its maximum in Tertiary, when huge stone masses emerged from the sea. This is when chained mountains were formed, amongst other, Velebit. Pressures from Africa towards Europe last even nowadays, which confirms the excessive seismical activity in the karst area.
THE GEOLOGICAL STRUCTURE OF THE NATIONAL PARK
By analysing the rocks on the National Park's surface, we can track down events that took place during the last 240 million years. 
The oldest rocks found on today's surface form the central area of the Štirovača valley. They were formed in former shoals in a period between 241 and 227 million years ago, by sedimentation of the algae limestones. That period was marked by the enhanced tectonic activity, during which cracking and thoring apart of the Earth's surface crust began.
In the separated parts, that were once shoals, deep, narrow troughs emanated. In the deepest parts of these troughs submarine volcano eruptions occured. Together with the lava flow, the process of settling down of volcanoclastic materials also took place. From that material were made tuffs, tuffits, hornstones and clastic rocks: shales and sandstones. 
At the end of Trias , the terrain started rising, the sea withdrew and former platform become land. The time of dilapidation and karsting of the arosen algae limestones begun.
In karst-formed valleys and sinkholes streams brought a variety of material which settled down on their bottoms. They were painted red, due to the high amount of iron and alluminium oxides. From their debris, the rocks were formed: clay shales, sandstones and conglomerates. Today, these rocks can be easely found on the valley's flanks and its northern parts.
|
The mainland regime lasted between 10 and 14 million years, almost until the end of Trias, when entire area was again overwhelmed by the sea. The deposition of carbonates continued. Carbon rocks from that era - dolomites - can be seen on the wider area of Štirovača. The largest masses of carbonates in the Park were deposited in the geological era of Jurassic . That was also the time of the greatest expansion of the biggest land and sea animals in the Earth's history. By the beginning of that period, some 205 million years ago, a very important event for the Adriatic carbonic platform took place - it was separated from the northern uppermost part of Africa, that is, become independent, and started its journey as an independet mainland system towards north - Europe.
Some 180 million years ago, Apullian and Apenninian platforms were separated from the Adriatic platform. Slowly, between the Adriatic and the Italian platform a deep sea path was widened and deepened, in geology known as the Ionic-Middleadriatic-Belundic basin.
That event is connected with the global separation of North America from Europe and Africa, which means opening, i.e. forming of the Atlantic Ocean.
That line of events drew the frontiers of our platform, which will remain unchanged until the Mesosoic era. In the late Jurrasic era, the African continent starts approaching Europe more intensively, which is manifested in strong tectonic movements towards our platform. It begins to twist and bend, i.e. to wrinkle. The Jurrasic rocks are today visible in the east of Cipala, Zavižan, Ruje and Lom, while on the south they stretch from Mali Ledge and Seravski Peak.
Some 142 million years ago, the intensive fluctuation of sea level and local tectonic movements occured. African impacts on the Adriatic platform become more powerful, which effected the platform's morphology. Due to the compression, it wrinkles and becomes more wave-like. Rocks from that period were not discovered on the surface of the Park.
65 million years ago, at the end of Cretaceous, the entire territory started to rise and transform into mainland. Only the today's coastal areas remained under sea, and inside them the foraminiferal limestones were deposited.
By the beginning of the Paleogenic, some 45 million years ago, strong African pressures occured again. This time, they caused the formation of the Dinaridian mountain chain, which includes Velebit. Since then, the intensive process of destruction, dilapidation and erosion of Velebit begun. Huge amounts of rock material were swooped along steep cliffs inside the ancient shoals and valleys. Large and smaller stone pieces of different ages (Jurrasic, Cretaceous or Paleogenic), as well as the excessive amount of the small-grained material brought by streams from remote areas had been transformed and cemented through millions of years, thus forming a new rock which the geologist today call the breccia jelar. 
The fact that rocks that today form some of the highest Velebit's peaks were concieved in valleys and shoals clearly shows how strong and powerful were the geological processes - raising, wrinkling, cracking and breaking of the ancient stone masses in the past.
Coastal slopes, Smrčeve doline (Spruce Valleys), Rožanski and Hajdučki Ledges consist of these rocks.
|
