(SI) Pred 220 milijoni let, je ob poti iz Godoviča na Medvedje Brdo, svoje sledi pustila neznana žival, eden prvih dinozavrov ali njihov predhodnik. V plasti dolomita so se ohranile doslej edine odkrite fosilne stopinje v Sloveniji.
PRED ZACETKOM:
Opis tega Geološkega zaklada je dolg. Prosimo, preberite ga in si zapisite naloge za vpis se pred obiskom zaklada!
NALOGE ZA VPIS OBISKA
1. Na zacetku in na koncu sledi si oglejte lego plasti dolomita v kateri so odtisnjene stopinje.
a) Kaj menite, ali je mozno, da bo nekoc v prihodnosti razkrito se nadaljevanje okamenele sledi v eno smer? Obrazlozite svoje mnenje.
b) Vsaj v eno smer nadaljevanja sledi nikoli vec ne bo mozno odkriti. Zakaj?
2. Pozorno si oglejte robove posameznih stopinj. Ali so robovi v isti ravnini kot povrsina dolomitne plasti v kateri se nahajajo ali so dvignjeni nad to povrsino? Obrazlozite zakaj je tako.
POMEMBNO!
- Preden vpisete obisk zaklada, posljite odgovore preko GC profila ali neposredno na e-naslov vane.si.geo@gmail.com. Takoj potem lahko vpisete obisk zaklada na spletu – ne potrebujete dodatnega dovoljenja. Ce ste fotografirali, prosimo, prilozite kaksno fotografijo.
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- Vpisi, ki vsebujejo odgovor bodo izbrisani!
(ENG) 220 million years ago, one of the earliest dinosaurs or one of their ancestors left its footprints at the trail from Godovič to Medvedje Brdo. Dolomite rock layers preserved them to this day. This is the only known fossil footprints location in Slovenia.
BEFORE THE BEGINNING:
This EarthCache has a long description! Please, read it and write down logging tasks before visiting the EarthCache site!
LOGGING TASKS
1. Take a look of the dolomite layer at the beginning of the footprints-trail and at the end of it.
a) What do you think: is it possible that the continuation of the footprints-trail would be disclosed sometimes in the future? Explain your opinion.
b) It will not be possible to uncover the continuation of the footprints-trail at least at one side of the trail anymore. Why?
2. Take a close look at the edges of the individual footprint. Are the edges in the same level as surface of the layer which contains footprints, or are the edges raised above this level? Why?
IMPORTANT!
- Send answers through GC profile or directly to e-mail vane.si.geo@gmail.com
before logging. After that you can log - you don't need an additional permission to log. Please, upload photos if you have taken them.
- Logs without an accompanying e-mail containing correct answers will be encrypted and later deleted!
- Logs containing the answer will be deleted!
slovensko besedilo / Slovenian text
tocke poti in dnevniki / waypoints and logs
Visit our web-site Geološki zakladi / EarthCaches
for a complete list of our EarthCaches and a lot of additional information.
(ENG) MEDVEDJE BRDO (BEAR HILL) AND BEAR FOOTPRINTS
There are two possible origins of the village name Medvedje Brdo (translated: Bear Hill). One says it is derived from med-vodje brdo. This could be translated as between-two waters, which is true, since Medvedje Brdo is situated at the watershed. Part of waters flow to Adriatic, the other part to Black sea. And than, the story says, somebody has met a bear (medved in Slovenian)… This event changed the name from Medvodje to Medvedje.
“Holes” in the surface of the open rock layer near farm Pesek are known for a long time to the locals. They have named them “bear’s feet” and probably also made a story or two about them. The real story about those footprints has begun to unfold in 1989, when Slovenian Museum of Natural History has been informed about them. Paleontologists have made several visits of the location and determined that footprints are imprinted in the layer of dolomite, which is probably of Triassic age.
PALEONTOLOGICAL EXPLANATION OF FOOTPRINTS
(Conclusions of Prof. Jernej Pavsic (published in magazine Gea, 1993):
“Detailed survey and additional analyses of rocks in the laboratory shoe that footprints have been mad in Upper Triassic, about 220 million years ago. They are imprinted in the dolomite layer, which is almost horizontal, with slight incline towards northwest. Trail is represented with six footprints, leading from northeast towards southwest. Their diameter is about 12 cm. Form of individual prints is problematic, since weather and weathering have made some damage. Therefore we can only guess that it has been a three-toes-foot animal - it could have got more toes... Prints are placed in the uniform distance of 32 cm, complete trail is about 130 cm long.
It is hard to determine which animal has made these footprints. There have not been many large land animals beside reptiles at that time. It has undoubtedly been a biped reptile, which has not been large according to footprints – maybe of human-size. It has probably been an ancestor of the dinosaurs, since dinosaurs have only beginning their 160 million years of dominion. The environment in which prints have been made has probably been similar to modern lagoons. Animals walked at soft dolomite mud in the intratidal zone or in shallow lagoon water. We can only guess what they have been doing there – maybe feeding with coastal mollusks or have been just passing the territory which preserved their footprints to this day.”
Figure 1: Sketch of biped reptile which has supposedly left its footprints above Godovic. Drawn by Marjan Grm, according to paleontologist’s concept (Pavsic, 1993).
ARE THOSE REAL FOOTPRINTS?
Some geologists started to doubt about paleontologists conclusions. The main reason has been the present position of the stone layers with footprints, since, according to geologic map made by Ivan Mlakar in 1969, those layers are supposed to be in inverse position, in other words, turned upside-down!
Geologists talk about the normal position of strata when layers preserved the position in which they have been formed. Because of tectonic displacements layers can also be turned upside-down. In this case they talk about the inverse position of strata.
So, if the layers above Godovic are in the inverse position, they have been turned upside-down and today’s surface has been at the bottom of the layer originally. In this case holes in the dolomite could only be imprints of the raised parts of the layer which has been positioned beneath, and not animal footprints at all! Therefore inverse or normal position is crucial for the explanation of the animal-origin of the imprints.
GEOLOGIC INVESTIGATORS AT WORK
Footprints location has not been thoroughly researched, and unprotected for a long time. Public interest has been high and footprints attracted many visitors, also those unwanted, who partly damaged priceless heritage. Only in 2004, detailed geologic survey has been done, structure-lithologic map of immediate surrounding made, many forms in sedimentary rock layers observed, and samples gathered for further examination (Skaberne, Car, 2004).
In the case of footprints we can compare geologic survey directly to criminal investigation, including detailed examination of the “crime scene” and later forensic research in the laboratory. Find out how geologists found the culprit responsible for the footprints in dolomite.
HOW CAN GEOLOGISTS DETERMINE POSITION OF ROCK LAYERS AT THE TIME OF FORMATION?
In the local rock they have visually observed many layers separated by gaps. There are visible forms called stromatolites in many places inside the layers. Modern observation data tells that stromatolites form in the supratidal and intratidal zones, when mud is glued on slippery cover of cyanobacteria in warm, tropical seas. Lime mud is often left above sea water in the supratidal zone and starts to dry. Mud contracts in the process of drying and more or less horizontal empty little cavities, named desiccation pores form. Dried mud is again flooded by seawater later, and desiccation pores too.
Very fine-grained lime mud, also called micrite (in the case of calcareous particles) and dolomicrite (in the case of dolomite) is deposited from seawater. Lime mud can partially fill desiccation pores and covers the bottom of small cavities in the form of very thin horizontal layers. In this case, geologists talk about micritic internal carbonate sediment. Desiccation pores with mictitic inner carbonate sediment are called geopetal structures. Since those structures formed in horizontal position, they can very convincingly show original position of layers.
Figure 2: Examination of sanded samples in laboratory: 2a: Typical stromatolite horizon with dissection pores (fine light parts in the darker stone background). 2b: Upper Triassic Norian-Rhaetian dolomite. Lower part is coars-grained, upper and darker part is more fine-grained with more bituminoze substance.
Visual examination of the rock layers in-situ also provides some important information. At the upper surface of dolomite rock layers many small moundlike structures have been observed, which have been formed by sea currents and waves with depositing and shifting fine-grained sediments. Moundlike structures can form only on the surface of the rock layers and are easily recognizable, because of their raised, mound-like shape. These structures therefore undoubtedly determine normal or inverse position of dolomite layers.
Figure 3: Visual examination of rock layers in-situ: 3a: upper Triassic Norian-Rhaetian dolomite. Thickness of layers is very variable. 3b: Moundlike structure – left from the pencil. Bottom of the layer is flat, upper surface of the same layer is typically moundlike shaped. Smaller moundlike structures are also visible in the upper part of the picture. Photo: Joze Car, reference No. 1.
FOOTPRINTS ARE NOT VERY SHARP. WHY?
Short explanation first: Diagenesis is a long and complicated process starting at the time of deposition of material and lasts until the rock begins to be transformed because of pressure and high temperature deeper in the Earth crust, or/and the rock is tectonically lifted to the surface and exposed to the weathering. Early diagenetic processes are those which change soft sediments to the solid sedimentary rock. Late diagenetic processes are all processes happening in the solid rock until it is exposed to weathering of metamorphism.
The nature or examined dolomite is variable from one layer to another. Upper Triassic Norian-Rhaetian dolomite has been formed by early diagenetic processes. Therefore, lime mud soon after the deposition transformed to dolomite rock in the process of dolomitisation. Some parts of the rock has been recrystalised in later periods (finer dolomite crystals transform into larger) and some crystals have also been replaced with quartz. These late diagenetic processes are to blame for changing of the reptile footprints, which are not exactly sharp-edged any more.
WHAT HAVE BEEN THE “CRIME” CIRCUMSTANCES AND WHO IS “TO BLAME”?
Conclusions of Joze Car and Dragomir Skaberne:
1. Location in the immediate surroundings of Pesek farm is build by Upper Triassic Norian-Rhaetian dolomite, of so called Cekovnik nappe (Mlakar 1969, Placer 1981). Rocks present an overthrust over Lower Cretaceous limeston of Kosevnik nappe.
2. Normal position of Norian-Rhaetian dolomite is proved by general data from geological survey, macroscopic examination (stromatolite lamination, three-dimensional moundlike structures), and microscopic textures (geopetal structures in desiccation pores).
3. Footprints near Pesek farm are therefore track of the reptile, in agreement with paleontologists conclusions.
Figure 4: _ Reptile is walking on the soft mud of the warm tropical lagoon; - Footprints have been made; - Footprints have been filled with sea sediments, which turned into the rock through millions of years; - Rock layers with preserved fossil footprints have been at the surface again, rock which filled the prints has been removed. Reference No. 3.
THE FOSSILE FOOTPRINTS ARE A PRECIOUS TREASURE OF NATURAL HISTORY
Footprints location is marked and equipped with an explanatory board since 2004. The unique geological profile has a status of the nature heritage of national importance today.
Already during first research a cast of the footprints has been made. It is now at display in the Slovenian Museum of Natural History.
EARTHCACHE AND ACCESS
EarthCache coordinates are set at the site of the footprints. You can access the site from Godovic or from Rovte and Medvedje Brdo. Use waypoints for help. You can park a car close to the site. If you preered some walk, park at waypoint W2.
Please, don’t trade across the footprints track and don’t try to collect samples on the site!
Access to the site is unlimited and free of charge.
References:
1. Skaberne and Car, 2004: Reptile footprints at Pesek farm above Godovic (Odtisi reptilovih stopinj pri kmetiji Pesek nad Godovicem), Idrijski razgledi 49/2-2004, Mestni muzej Idrija, Idrija.
2. Pavsic, J., 1993: The footsteps above Godovic (Stopinje nad Godovicem), magazine GEA, 36-37, Ljubljana.
3. Information board at the site of the fossile footprintsj. Sketch: Jurij Mikuletic, text: Martina Stupar, The Institute of the Republic of Slovenia for Nature Conservation.
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MEDVEDJE BRDO IN MEDVEDOVE STOPINJE
Ime zaselka, oziroma soseske ima po pripovedovanju domacinov dva izvora. Eno izrocilo pravi, da izhaja danasnje ime iz zlozenke med-vodje brdo. Vcasih so namrec Medvedjemu Brdu rekli kar Medvodje. Najbrz zato, ker je zaselek na razvodju. Del potokov se zbira v reke, ki se stekajo v Savo, preostalo pa v vode in reke, ki vodijo v Jadransko morje. Potem pa, pravi izrocilo, je nekdo nekoc srecal medveda…
Vdolbine v razkritih plasteh kamnin, v blizini kmetije Pesek, so domacinom ze dolgo znane. Rekli so jim 'medvedove tace' in v zvezi z njimi verjetno spletli tudi kaksno zgodbo. A resnicna zgodba o sledeh se je zacela razpletati sele leta 1989, ko so o stopinjah neznane zivali v dolomitu obvestili Prirodoslovni muzej Slovenije. Po veckratnem ogledu so paleontologi ugotovili, da se odtisi nahajajo na plosci dolomita, verjetno zgornjetriasne starosti.
PALEONTOLOSKA RAZLAGA STOPINJ
Zakljucki prof. dr. Jerneja Pavsica (objavljeni v revija Gea, 1993):
»Podroben ogled stopinj in kasnejse analize kamnin v laboratoriju, so pokazale, da so stopinje nastale v zgornjem triasu, pred priblizno 220 milijoni let. Odtisnjene so v kamniti dolomitni plosci, ki vpada proti severozahodu in je skoraj vodoravna. Sled predstavlja zaporedje stopinj, ki potekajo od severovzhoda proti jugozahodu. Njihov premer je okrog 12 centimetrov. Oblika sledi je precej problematicna, kajti vremenski vplivi so opravili svoje. Sledi so tako zlizane, da lahko le ugibamo, ali gre za troprsto ali vecprsto sled... Med seboj so stopinje enakomerno oddaljene po 32 centimetrov, skupna dolzina sledi je priblizno 130 centimetrov.
Kateri zivali so sledovi pripadali, je tezko zanesljivo povedati. V tistem casu poleg kuscarjev ni bilo drugih vecjih kopenskih zivali. Nedvomno je, da gre za dvonoznega kuscarja, ki glede na velikost odtisov stopal ni bil posebno velik, morda cloveske velikosti. Verjetno je pripadal predhodnikom dinozavrov, ki so prav v tem casu zacenjali 160 milijonov let dolgo zgodovino. Okolje, v katerem so se ohranile sledi, je bilo po vsej verjetnosti podobno danasnjim lagunam. Hodili so po mehkem dolomitnem blatu v medplimskem pasu ali plitvi vodi lagune. Kaj so tam poceli, lahko zopet samo ugibamo, morda so se hranili z obalnimi mehkuzci ali rastlinjem ali so se povsem slucajno znasli v tem okolju, ki je ohranilo njihove sledi do danasnjih dni.«
Slika 1: Skica dvonogega plazilca, ki naj bi pustil nad Godovicem najdene odtise. Skico je po zamisli paleontologov izdelal Marjan Grm (Pavsic, 1993).
ALI SO SLEDOVI V RESNICI LE IGRA NARAVE?
Ugotovitve paleontologov pa so bile po mnenju nekaterih strokovnjakov dvomljive. Predvsem zaradi lege kamninskih plasti s sledovi, oziroma glede na to kako so plasti obrnjene. Po geoloski karti dr. Ivana Mlakarja iz leta 1969, naj bi namrec plasti lezale v obrnjeni (inverzni) legi!
O normalni legi kamninskih plasti govorimo takrat, kadar lezijo kamnine danes v naravi tako kot so v davni geoloski preteklosti nastale. Zaradi tektonskih premikanj pa so lahko kamnine postavljene tudi na glavo, oziroma obrnjene, v takih primerih govorimo o obrnjeni ali inverzni legi plasti.
V kolikor so plasti nad Godovicem inverzne, so prvotno lezale zasukane, torej je bila sedanja povrsina s sledovi na spodnji strani. V tem primeru so vdolbine lahko le odtisi dvignjenih delov plasti, ki so lezale pod njimi in ne pravi sledovi zivali. Normalna ali inverzna lega plasti ima torej odlocilno vlogo pri ugotovitvi, ali gre v resnici lahko za odtise nog ali le splet drugih naravnih procesov.
GEOLOSKI DETEKTIVI NA DELU
Obmocje sledov je dolgo ostalo brez podrobnejsih raziskav in nezasciteno. Zaradi velikega zanimanja, so sledovi privabili stevilne obiskovalce, zal tudi neosvescene, ki so neprecenljivo dediscino tudi delno poskodovali. Sele leta 2004 je bilo izvedeno geolosko kartiranje, izdelana je bila strukturno litoloska karta obmocja, opazovane stevilne oblike v sedimentnih plasteh kamnine in nabranih nekaj vzorcev kamnin za analize (Skaberne, Car, 2004).
V nasem primeru lahko geolosko raziskavo primerjamo kar z delom detektivov in forenzikov. Vkljucno z ogledom »mesta zlocina« na terenu in kasnejsimi raziskavami v laboratoriju. Preberite si kako so geologi dolocili krivca za sledi v dolomitu.
KAKO GEOLOGI UGOTOVIJO PRVOTNO LEGO KAMNINSKIH PLASTI?
S prostim ocesom so v preiskani kamnini opazovali stevilne plasti, ki so med seboj locene s prekinitvami - lezikami. Znotraj plasti so na stevilnih mestih vidne oblike, imenovane stromatoliti. Iz danasnjih opazovanj vemo, da stromatoliti nastajajo v medplimsko-nadplimskem okolju, z lovljenjem karbonatnega blata na sluzaste prevleke cianobakterij, ki odlicno uspevajo v toplih tropskih morjih. Ker je karbonatno blato pogosto na suhem, torej v nadplimskem obmocju, se zacne na zraku susiti. Pri tem se krci in v njem nastajajo bolj ali manj vodoravne prazne votlinice, ki jih imenujemo izsusitvene pore. Ko kasneje presuseno blato ponovno preplavi morska voda, zalije tudi izsusitvene pore.
Iz morske vode se lahko useda zelo drobnozrnato karbonatno blato, ki se strokovno imenuje mikrit (ce gre za kalcit ali apnenec) ali dolomikrit (ce gre za dolomit). Karbonatno blato lahko delno zapolni izsusitvene pore in prekrije dno votlinic v obliki horizontalno odlozenih, zelo tankih plasti. V takih primerih govorimo o mikritnem notranjem karbonatnem sedimentu. Izsusitvene pore z mikritnim notranjim sedimentom imenujemo geopetalne teksture. Ker so te strukture nastale v vodoravni legi, kot naravne vodne tehtnice zato zelo prepricljivo kazejo prvotno lego plasti.
Slika 2: Raziskava zbrusenih vzorcev v laboratoriju. 2a: Znacilen izgled stromatolitnega horizonta z izsusitvenimi porami (drobni svetlejsi deli v temnejsem delu kamnine). 2b: Zgornjetriasni norijsko-retijski dolomit. Spodnji svetlejsi del je debeleje zrnat, zgornji temnejsi del bolj drobnozrnat z vec bituminoznimi snovi. Na desni strani opazimo bocno izklinjanje manjse sipinice. Foto: Miran Udovc; vir 1.
Poleg nastetih oblik so med opazovanji kamninskih plasti na terenu v dolomitnih kamninah nasli se stevilne sipine in sipinice, ki so jih oblikovali morski tokovi in valovi z nanasanjem in prekladanjem drobnozrnatega morskega sedimenta. V kamninah se sipinice kazejo kot pravilno oblikovani dvignjeni kupolasti deli, ki nastajajo izkljucno na zgornjih povrsinah plasti. Torej tudi na podlagi sipinic in sipin lahko nesporno dolocijo normalno ali inverzno lego plasti norijsko-retijskega dolomita.
Slika 3: Raziskava na terenu. 3a: Plastnat zgornjetriasni norijsko-retijski dolomit. Debeline plasti se bocno spreminjajo. 3b: Sipinasto oblikovana plast – levo od svincnika. Spodaj je plast ravna, zgoraj pa znacilno kupolasto oblikovana. Manjse sipinice so vidne tudi v zgornjem delu slike. Foto: Joze Car; vir 1.
ZAKAJ NISO SLEDOVI BOLJ RAZLOCNI?
Najprej kratka razlaga: Diageneza je dolg in zapleten proces, ki se zacenja v trenutku, ko se material v nekem okolju odlozi (kopno, reka, jezero, morje ipd), pa vse do trenutka, ko se zacne kamnina zaradi pritiskov in visokih temperatur v globljih delih zemeljske skorje spreminjati, metamorfozirati in/ali do obdobja, ko kamnino tektonske sile dvignejo v blizino povrsine in so izpostavljene povrsinskim spremembam, preperevanju. Med zgodnjediagenetske procese pristevamo vse fizikalno-kemijske dogodke, pri katerih se mehki sedimenti (usedline) spremenijo v trdno sedimentno kamnino. K poznodiagenetskim procesom pa stejemo vse, ki se dogodijo ze v trdni kamnini, dokler ne nastopijo metamorfni procesi.
Znacaj preiskovanega dolomita se od plasti do plasti spreminja, tako navzgor kot tudi v bocni smeri. Zgornjetriasni norijsko-retijski dolomit je zgodnje diagenetskega nastanka, kar pomeni, da je morsko apnencevo blato, po katerem se je sprehajal dvonogi reptil, kmalu po odlozitvi v procesih dolomitizacije preslo v dolomitno kamnino. Ta je bila v kasnejsih geoloskih obdobjih, v tako imenovani pozni diagenezi, na stevilnih mestih prekristaljena (drobni dolomitni kristali prehajajo v vecje) in ponekod okremenjena (kristale dolomita je nadomestil kremen). Prav poznodiagenetske spremembe – prekristalizacija in okremenitev - so vzrok, da so se tudi odtisi plazilcevih 'tac' spremenili in niso povsem jasni.
KAKSNE SO BILE TOREJ OKOLISCINE »ZLOCINA« IN KDO JE »KRIVEC«?
Ugotovitve Jozeta Cara in Dragomirja Skaberneta:
1. Terene v neposredni okolici kmetije Pesek gradi plastnat zgornjetriasni norijsko-retijski dolomit, ki pripada tako imenovani Cekovniski vmesni luski (Mlakar, 1969; Placer, 1981). Kamnine lezijo v obliki velike plosce narivno na spodnjekrednih apnencih Kosevniske vmesne luske.
2. Normalno lego norijsko-retijskega dolomita dokazujejo splosni podatki geoloskega kartiranje ter makroskopske (stromatolitna laminacija, 3D sipinice) in mikroskopske teksture (geopetalne teksture v izsusitvenih porah).
3. Sledovi stopinj pri kmetiji Pesek so torej sledovi hoje reptila soglasno z ugotovitvami paleontologov.
Slika 4: - Noge so se vdirale v mehko blato; - Nastali so odtisi stopinj; - Odtise je zapolnil in prekril morski sediment, ki se je skozi milijone let spremenil v kamnino; - Kamnina z ohranjenimi fosilnimi odtisi je bila spet na povrsju, prvotna zapolnitev pa odstranjena. vir 3.
FOSILNI ODTISI SLEDI SO PRVOVRSTEN NARAVNI SPOMENIK!
Danes je lokacija z odtisi stopal oznacena in opremljena s pojasnjevalno tablo. Edinstveni geoloski profil ima od leta 2004 status naravne vrednote drzavnega pomena.
Ze v casu prvih raziskav so bili izdelani tudi odlitki odtisov, ki so na ogled obiskovalcem Prirodoslovnega muzeja v Ljubljani.
GEOLOŠKI ZAKLAD IN DOSTOP
Koordinate Geološkega zaklada so postavljene na lokacijo fosilnih odtisov. Do tja se lahko pripeljete iz Godovica ali preko Rovt in Medvedjega Brda. Za pomoc so vam lahko tocke poti. Avto lahko parkirate v blizini odtisov, ce pa vam je ljubsi sprehod, parkirajte pri tocki poti W2.
Prosimo, ne hodite preko sledi in ne poskusajte odvzemati vzorcev kamnine!
Viri:
1. Skaberne in Car, 2004: Odtisi reptilovih stopinj pri kmetiji Pesek nad Godovicem, Idrijski razgledi 49/2-2004, Mestni muzej Idrija, Idrija.
2. Pavsic, J., 1 993: Stopinje nad Godovicem, Geina sredica, GEA, 36-37, Ljubljana.
3. Informacijska tabla na mestu fosilnih odtisov stopinj. Risba: Jurij Mikuletic, besedilo: Martina Stupar, Zavod RS za varstvo narave.
tocke poti in dnevniki / waypoints and logs