Historija dva bunara
Trg Sv. Trojstva u Tvrđi je jedan od najstarijih Osječkih trgova. Na trgu su 1751. godine postavljena dva javna kamena bunara u baroknom stilu. Služili su za napajanje konja, tada neizbježnih za vojne i ine potrebe. Dvije vodene pumpe uz obalu Drave opskrbile su vodom kroz vodovodne cijevi te dva bunara. Ovo pokriva nekoliko godina povijesti. Kopajmo dublje.
Povijest vapnenca
Bunari na trgu izgrađeni su od žilavog vapnenca iz Mađarske. Vapnenac je sedimentna stijena biološkog podrijetla koja se formirala na dnu mora prije stotina milijuna godina - riječ je o bivšim koraljnim grebenima, nakupinama školjaka, kostiju i slično. Tako nastali vapnenac naziva se biološkim vapnencem. Biološko podrijetlo vapnenca jasno potvrđuje prisutnost fosila. Ponekad, iako rijetko, vapnenac može nastati i izravnim taloženjem minerala iz vode, u kojem slučaju ga nazivamo kemijskim vapnencem. Takvi vapnenci su prilično rijetki na Zemljinoj površini te općenito imaju zanimljive oblike, posebice u prirodnim špiljama. No, usmjerimo se na biološki vapnenac.
Fosili
Pod fosilima podrazumijevamo sve očuvane ostatke, otiske ili tragove bilo kojeg živog organizma iz prošlih geoloških razdoblja. Fosili mogu pružiti izravne ili neizravne dokaze o drevnom životu. Izravni dokazi znače fosilizirane ostatke organizama, kosti, kutije. Ili okamenjeno drvo, dijelove lišća i slično. Neizravni dokazi života znače fosilizirane tragove, staze ili oznake koje su ostavili organizmi. Neuobičajen neizravan dokaz drevnog života može biti na primjer koprolit - fosilizirani izmet. Na bunarima ćete zasigurno pronaći fosile amonita. Amoniti su izumrla skupina morskih životinja. Pojavljivali su se uglavnom u morima Devon - Kreda prije otprilike 425-65 milijuna godina. Karakteristični su po zakrivljenoj spiralnoj kutiji veličine od nekoliko milimetara do 2 metra. Unutar tijela imali su pregrade koje su odvajale komore ispunjene plinom što je omogućavalo slobod.
Zadaci
Prije nego zabilježite nalaz earth cache, morate poslati poruku s točnim odgovorima na pitanja. Bilježenje earth cachea trebate obaviti odmah nakon slanja odgovora. Izbrisat ću zapise bez odgovora. Kratke upute za uporabu: šaljem odgovore, a zatim bilježim earth cache. Ako se ne slažete s ovim zahtjevom, molimo vas da ne bilježite ovaj earth cache. Za detalje o zahtjevima za earth cache pogledajte ovde.
Pretražite dva bunara kako biste pronašli fosile i promatrali ih, zatim odgovorite na tri pitanja:
- Opišite boju ovog vapnenca.
- Pružaju li ovi fosili izravan ili neizravan dokaz o drevnim organizmima? Objasnite zašto.
- Pronađite najveći fosil i pošaljite mi njegovu veličinu u centimetrima. Možete procijeniti.
- NEobjavljujte fotografije fosila u vašem zapisu.
The history of two wells
Square of Holy Trinity in Fortress is one of the oldest squares in Osijek. In 1751, two public stone wells in the Baroque style were installed on the square. They served to feed the horses, which were then crucial for military and other needs. Two water pumps along the banks of the river Drava supplied water through water pipes to those two wells. This covers few years of history. Let's dig deeper.
History of limestone
The wells in the square were built of unpolished red tuberous limestone from Hungary. Limestone is a sedimentary rock of biological origin that was formed on the bottom of the sea hundreds of millions of years ago - we are talking about former coral reefs, accumulations of shells, bones etc... So created limestone is called biological. The biological origin of the limestone is clearly confirmed by the presence of fossils. Sometimes, although rarely, limestone can also be formed by direct precipitation of minerals from water, in which case we call it chemical limestone. Such limestones are quite rare on the Earth's surface and generally have interesting shapes, especially in caves. But let's focus on biological limestone.
Fossils
Under fossil we mean any preserved remain, imprint or trace of any living organism of the past geological age. Fossils can provide direct or indirect evidence of ancient life. Direct evidence means the fossilized residue of organisms, bones, boxes. Or petrified wood, parts of leaves and similar. Indirect evidence of life means fossilized traces, paths or marks left by organisms. An unusual indirect proof of ancient life can be for example coprolite - fossilized feces. You will certainly find fossils of ammonites at the wells. Ammonites are an extinct group of marine animals. They appeared mainly in the Devonian - Cretaceous seas about 425-65 million years ago. Characteristic for them is a curved spiral box with dimensions from a few millimeters up to 2 meters. There were dividing walls separating the chambers filled with gas which allowed free-floating of animal. See picture above for example of ammonite.
Logging tasks
Before you log the earth cache you have to send the correct answers to the questions. Reply via my profile. Logging the earth cache should be done right after sending the answers. I will delete the logs without answers. Brief instructions for use: I send answers and then I log the earth cache.
For details on earth cache requirements, see here.
Search the two wells to find fossils and observe them, then answer three questions:
- Describe the color of this limestone.
- Do these fossils provide direct or indirect evidence of ancient organisms? Explain why.
- Find the largest fossil and send me its size in centimeters. You can estimate.
- DO NOT post photos of fossil in your post.