Geološko-paleontološki rezervat Crnika EarthCache

Plaža Crnika jedno je od najznačajnijih paleontoloških nalazišta u Hrvatskoj, jedini lokalitet u hrvatskom priobalju gdje su izložene naslage miocenske starosti. / Crnika beach is one of the most important paleontological sites in Croatia, the only area in the Croatian coastal region where exposed sediments from the Miocene age can be seen.

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Plaža Crnika je jedini lokalitet na hrvatskom priobalju na kojem su izložene naslage miocenske starosti s ostacima izumrlih životinjskih zajednica te predstavlja potencijalni locus typicus za slatkovodni miocen Jadrana. Istraživanjima je utvrđeno kako je otok Pag nekada bio močvarno područje uz jezero na kojem su živjeli krokodili, mali sisavci, školjkaši, ribe, a sve je bilo prekriveno gustim močvarnim biljem. Na ovom su predjelu pronađene dvadeset milijuna godina stare miocenske naslage. Plaža Crnika je također bogato paleontološko nalazište.

Crnika je istraživana u nekoliko navrata. Prvi je put istraživana još u 19. stoljeću, kad su tražili pogodna nalazišta za eksploataciju ugljena. Austrijski inženjeri naišli su na zanimljive fosilne ostatke u ugljenu i u slojevima iznad i ispod njega. Crnika je opet istraživana od 1988. do 1990. godine u okviru naftnogeoloških istraživanja. Hrvatski su geolozi za pronađene fosile ustvrdili, da se radi o miocenskim naslagama. Istraživanja u svrhu zaštite konačno su započeta 2001. godine i pronađeni su brojni fosili iz razdoblja miocena, stari oko 18 milijuna godina.

Crnika je važna jer samo na njoj ima tragova miocenske starosti. Prijelaz je između pradavnih jezera s kontinenta i prostora prema Apeninskom poluotoku. Pretpostavlja se, da je prostor do Dugog otoka u miocenu bio morski prostor, jedno drevno jezero koje je najvjerojatnije s morem bilo povezano rukavcima. Zbog toga se u njemu miješala morska i slatka voda. Nalazi ugljena potvrđuju tezu o bujnoj vegetaciji. Zbog močvare, stajaće vode koja je tu bila, bili su anoksični uvjeti. Pali biljni materijal sačuvao se, vremenom su ga prekrili drugi materijali kao lapor te se drvena masa pretvorila u ugljen.

Geokemijski proces koji se događao na plaži, u kojem su se stvarale naslage, sadržavao je ljušturice školjaka i njihove kalupe. Od njih su nastali čitavi slojevi, debljine oko trideset centimetara. Nalazište ne završava Crnikom, nego se pruža prema kopnenom dijelu. Najstariji nalazi su u smjeru grada Paga. Slojevi naslaga padaju prema sjeverozapadu.

Na lokalitetu su pronađeni ostaci više od trideset biljnih i životinjskih vrsta, od kojih su posebno zanimljivi zub krokodila i fosil puža roda Valvata. Pronađene su ljušture različitih vrsta puževa i školjkaša, ostaci bilja, te rijetki nalazi malih sisavaca. Nalaz puža Valvata sa značajkama podroda Costavalvata u miocenskim naslagama Crnike prvi je nalaz tog oblika u fosiliziranom stanju.

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Crnika beach is the only area in the Croatian coastal region where sediments from the Miocene era, containing remains of extinct animals, can be seen and represents a potential locus typicus for freshwater Miocene in the Adriatic. Research in this area showed that the island of Pag was once a marshy area along a lake where crocodiles, small mammals, shellfish and fish lived, and everything was covered in dense wetland vegetation. Sediments found here are around 20 million years old. Crnika beach is also a rich paleontological site.

Crnika was researched several times. It was first studied in the 19th century, while searching for suitable sites for the exploitation of coal. Austrian engineers ran into interesting fossil remains in coal and in the layers above and below it. Crnika was again investigated from 1988 to 1990 in petroleum exploration. Croatian geologists confirmed that the found fossils were from Miocene sediments. Research for the protection of the site finally started in 2001 and numerous fossils from the Miocene period, about 18 million years ago, were found.

Crnika beach is important beacuse it is the only site in Croatia with traces from the Miocene age, when it was the transition between the ancient continental lakes and the space towards the Apennine peninsula. It is assumed that the space up to Dugi otok was a sea area during the Miocene age - an ancient lake that was most likely connected to the sea with backwaters. This is where sea and fresh water mixed together. The presence of coal in this location confirms the theory of lush vegetation. Because of swamps and stagnant water that were there, the conditions were anoxic. Fallen plant material was preserved, over time it was covered by other materials such as marl and the wood turned into coal.

The geochemical process that was happening on the beach, which created layers of sediments, preserved the shells and their molds. They developed into whole layers, about 30 cm or one foot thick. The site does not end at the beach, but extends to the mainland area, with the oldest specimens in the direction of the town of Pag. Layers of sediments fall in the northwest direction.

Remains of more than thirty plant and animal species were found at the site, the most interesting among them are a tooth of a crocodile and the fossil of a Valvata snail. Among other finds were the shells od different species of snails and shellfish, the remains of plants and rare finds of small mammals. Finding of a Valvata snail with features of the subgenus Costavalvata in the Crnika Miocene sediments is the first finding of its kind in the fossilized state.

To log this EarthCache, please answer the following questions:

1. While approaching the EarthCache location, pay attention to the rocks on the path. Describe what stands out in connection to the EarthCache description.

2. At the EarthCache coordinates take a look at the cliff before you. Estimate its height. Describe the apperance of the sediments - what colours can you see, direction of the sediments etc. Find the 7coal layer in the sediments - estimate its thickness. What colours are the layers above and below the coal?

3. By looking at the cliff can you see any fossils in the sediments? (Do not dig or in any way destroy the cliff!)

4. Turn to the sea and look at the sea bed at the coordinates. What can you observe?

5. In your own words explain why it was important that the waters, in which charcoal later formed, were calm and anoxic (i.e. containing little dissolved oxygen).

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