Fosilna morska obala
Širše območje Vač ter ozek pas proti Kleniku gradijo kamenine iz obdobja miocen, ki s svojo raznolikostjo razkrivajo del geološke preteklosti tega ozemlja. Največja zanimivost iz tega obdobja se nahaja nad pokopališčem na Vačah, kjer se nad travnikom dviguje približno 3 metre visoka navpična apnenčeva stena. Na tem mestu je jasno viden stik med sivim jurskim apnencem in rumenkasto miocensko drobnozrnato brečo (sprijeti ostri kamni) s peščenim vezivom. Ta del stene predstavlja razkriti ostanek nekdanje fosilne morske obale. V apnencu so se ohranili zelo redki sledovi školjk.
V Miocenu, to je nekako pred 13 miljoni let, so to strmo kamnito obalo, ki so jo na tem mestu gradili apnenci jurske starosti, nastali pred 210 miljoni let, poseljevale številne kamnovrtne školjke, iz rodu Lithophaga. Podobne školjke, znane kot prstac oziroma morski datelj, lahko najedemo še danes v slovenskem morju, kjer živijo le v večjih kamnih in skalah. Znano je, da te školjke izločajo kislino, s katero raztapljajo apnenec, tako da se z rastjo pomikajo vedno globje v kamen, vendar le toliko, da so zaščitene pred plenilci.
Luknje, ki so ostale kot dokaz delovanja kamnovrtnih školjk, so približno enako globoke, v nobeni ni ohranjena školjčna lupina, ker so bile zaradi valovanja in morskih tokov razlomljene in so izpadle iz kamnine že v miocenu ali pa sojih skozi dolga obdobja počasi raztapljale pronicajoče vode. V večji množini so na tem mestu ohranjene tudi fosilne školjčne lupine ostrig. So različno dobro ohranjene in velike do 10 centimetrov. Posamezne so še pritrjene na apnenčevo steno, tako kot so bile v času svojega življenja. Nekatere so tudi preluknjane od kamnovrtnih školjk, večinoma pa zaradi valovanja, ki je bilo očitno močno, razlomljene in se nahajajo v drobnozrnati breći, ki je nastala pod strmo obalo na ravnem dnu takratnega plitvega morja, kjer so se kopičili peščeni sedimenti s posameznimi ostrorobnimi odlomki kamenin.
Ostanek fosilne morske obale na Vačah je najlepši v Sloveniji in med najlepšimi na svetu. Zaradi pomembnosti je bil leta 1997 v Občini Litija, s sodelovanjem z Ljubljanskim regionalnim zavodom za varstvo naravne in kulturne dediščine, pripravljen odlok o razglasitvi geološke znamenitosti na Vačah za naravni spomenik. Tako je na tem mestu sedaj prepovedano odkopavati, lomiti, odnašati ali razbijati kamnine oz. okamnine, izvajati zemeljska dela, ki posredno ali neposredno prizadevajo geološki spomenik.
Za vpis zaklada, kot najdenega odgovorite na spodnja vprašanja in mi odgovore posredujete preko GC profila, vendar ni potrebno čakati na moj odgovor, da bi zaklad označili kot najden.
Vprašanja:
1. Poglejte fosilno morsko obalo. Oglejte si luknje, ki so ostale po kamnovrtnih školjkah, iz rodu Lithophagah. Ocenite približna velikost teh školk, glede na velikost lukenj?
2. Zakaj misliš, da je nad fosilno morsko obalo postavljena streha?
Neobvezno:
1. Vpisu lahko priložite tudi fotografije.
Viri:
http://www.vace.si/Fosilna_morska_obala.htm Informativna tabla
Fossilized sea shore
The wider area of Vače and the narrow strip towards Klenik build rocks from the Miocene period, which with their diversity reveal a part of the geological past of this territory. The greatest attraction from this period is located above the cemetery in Vače, where a vertical limestone wall about 3 meters high. At this point, the contact between the gray Jurassic limestone and the yellowish Miocene fine-grained breccia (attached sharp stones) with a sandy binder is clearly visible. This part of the wall represents the exposed remnant of a former fossil seashore. Very rare traces of shells have been preserved in the limestone.
In the Miocene, about 13 million years ago, this steep rocky shore, built on this site by Jurassic limestones formed 210 million years ago, was inhabited by numerous rock-like shells, of the genus Lithophaga. Similar shellfish, known as date shell, can still be found today in the Slovenian sea, where they live only in larger rocks and boulders. These shells are known to secrete the acid with which they dissolve limestone, so that as they grow they move deeper and deeper into the stone, but only so much as to protect them from predators.
The holes that remain as evidence of the operation of rock shells are about the same depth, no shell is preserved in them, because they were broken due to waves and sea currents and fell out of the rock already in the Miocene or soybeans slowly dissolved penetrating waters over long periods. Fossil shells of oysters are also preserved in large numbers at this site. They are variously well preserved and up to 10 centimeters in size. Individuals are still attached to the limestone wall, just as they were during their lifetime. Some are also perforated by rock shells, but mostly due to the wave, which was obviously strong, they are broken and are located in a fine-grained breccia, which formed under the steep shore on the flat bottom of the then shallow sea, where sandy sediments with individual sharp-edged fragments accumulated.
The remnant of the fossil sea coast in Vače is the most beautiful in Slovenia and among the most beautiful in the world. Due to its importance, a decree on declaring the geological site of Vače a natural monument was prepared in 1997 in the Municipality of Litija, in cooperation with the Ljubljana Regional Institute for the Protection of Natural and Cultural Heritage. Thus, it is now forbidden to excavate, break, carry away or break rocks at this place.
Here are the questions necessary for logging this cache as found. Please send the reply through the contact form, but do not wait for my reply, log right away.
Question:
1. Look at the fossilised seashore. Take a look at the holes left after the Lithophagah rock shells. What was approximate size of the shell according to the size of the holes?
2. Why do you think a roof is placed over the fossilised seashore?
Optional:
1. If you want you can make some photos and add them to your log.