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Ohessaare Limestones or Make a Wish

A cache by Elhana Send Message to Owner Message this owner
Hidden : 08/05/2010
Difficulty:
1.5 out of 5
Terrain:
1 out of 5

Size: Size: other (other)

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Geocache Description:


(EN) It is believed, that everyone, who will create stone pile in Ohessaare, can a make a wish and it will come true. Not a scientific fact, of course, but- who knows? So, lets learn about limestones first and then- have fun.

The limestone Ohessaare cliffs, on the western shores of the Sõrve peninsula, are around 500 m long and up to 4 m high. They present the most extensive cross-section of young Silurian rock and sedimentary layers in Estonia. The rocks in the area also contain a lot of fossils.
 
Limestone is a very common sedimentary rock of biochemical origin. It is composed mostly of the mineralcalcite. Sometimes it is almost pure calcite, but most limestones are filled with lots of other minerals and sand and they are called dirty limestones. The calcite is derived mostly from the remains of organisms such as clams, brachiopods, bryozoa, crinoids and corals. These animals live on the bottom of the sea and when they die their shells accumulate into piles of shelly debris. This debris can then form beds of limestone. Because of limestone's biogenic origins, it is often the best rock for finding fossils. The organisms themselves leave fossils in the rock and entire communities and even entire reef structures can be preserved in a limestone bed.
 
Limestone in Ohessaare is marine in origin and is often associated with other near shore rocks types.
 
In a typical marine scenario, to the shore side of a reef is the silica mud of a lagoon and closer to shore is the sand of a beach. The silica mud will form a shale while the beach sand will form a sandstone. Farther inland might be a swamp whose organic debris might form a coal layer. Throughout the Carboniferous time period, coals were often interbedded with sandstones, shales, and limestones in repeating cycles. These cycles represent changes in ocean levels over thousands of years as swamps are flooded by a beach and then a lagoon and perhaps a reef. But as sea levels fall the limestone of the reef is replaced by the shales of a lagoon and then the sandstone of a beach and on and on. Hundreds of feet of repeating cycles like this can occur.
 
Metamorphosed, fairly pure limestone forms the metamorphic rock, marble. During the metamorphic process, the crystals of fine grained calcite in the limestone become merged and melded into other large crystals forming the interlocking course grained texture of the marble.
 
Limestones are important rocks. They are less resistant than most igneous rocks, but more resistant than most other sedimentary rocks. They can be used for building materials but are easily weathered by acidic conditions. Rainwater picks up a small amount of carbon dioxide during its passage through the air, and that turns it into a very weak acid. Calcite is vulnerable to acid.
 
Along this Estonian shoreline you can also see boulders.
 
(EST) Rahvasuus usutakse, et igaüks, kes ehitab Ohessaare pangale kivikuhjakese, saab midagi soovida ning see täitub. Mõistagi ei ole see teaduslik fakt, kuid – äkki tõesti? Olgu, esmalt õpime lubjakivi tundma ja siis skoorime.
 
Paekivi ehk paas on karbonaatsete kivimite – lubjakivi, dolomiidi ja mergli üldnimetus. Tekkelt kuuluvad karbonaatkivimid biokeemiliste merepõhja setendite rühma. Tavalisim pae erim on lubjakivi, mille karbonaatsest osast moodustab kaltsiit (CaCO3) üle 50%, MgO sisaldus on kuni 14% ja lahustumatu jäägi sisaldus on kuni 25%. Tihti esineb lisanditena saviosakesi, glaukoniiti ja liiva. Lisanditest oleneb lubjakivi värvus, mis võib varieeruda valgest või kollakashallist kuni rohekani (http://www.ut.ee/BGGM/maavara/lubjakivi.html).
 
Sõrve poolsaare läänekaldal paiknev Ohessaare pank on ligi 500 m pikk ja kuni 4 m kõrge lubjakividest koosnev pangajärsak. Sellel pangal on nähtav kõige ulatuslikum läbilõige noorimate Siluri kivimite ja settekivimite kihtdest Eestis. Selle piirkonna kivid sisaldavad ka palju fossiile.
Lubjakivi on väga levinud biokeemiline settekivim. See koosneb peamiselt mineraalsest kaltsiidist. Mõnikord võib leida peaaegu puhast kaltsiiti, kuid enamik lubjakividest sisaldavad palju muid mineraale ja liiva, neid nimetatakse määrdunud lubjakiviks. Kaltsiit tekib peamiselt järgmiste organismide jäänustest: karbid, käsijalgsed, krinoiidid ja korallid. Need loomad elavad mere põhjas ja peale nende surma ladestuvad koorikud kuhjadesse. Need koorikurusud moodustavad lubjakivile nähtava kihi. Kuna lubjakivi on biogeenset päritolu, on ta parim kivi fossiilide leidmiseks. Lubjakivi lasunditest, mõnikord kogu rahu ulatuses, võib leida ka suuri kogukondi fossiiliks muutunud organisme.
 
Ohesaare lubjakivi on pärit merest ja sageli seotud ka teiste kivitüüpidega merekaldal.
Tüüpilise mereranna korral kalda poole vaadates näeme kõigepealt mudast laguuni ja lähemal liiva rannas. Ränidioksiidi sisaldav muda moodustab klindi nagu rannas liiv moodustab liivakivi. Kaugemal sisemaal võib soodes orgaanilisest ainest olla moodustunud söekiht. Karboni ajal oli süsi sageli segunenud liivakiviga, saviga ja lubjakiviga korduvates tsüklites. Need tsüklid esindavad muutusi ookeani tasemetes üle tuhandete aastate, kui sood olid üleujutatud rannad, millest hiljem tekkisid laguun ja ka riffid. Merevee taseme langedes asendus lubjakivi saviga ning liivaga, seda jälle uuesti ja uuesti. Nii ongi näha kümneid meetreid vahelduvaid kivimeid.
 
Laialt levinud moondekivimi on marmor. Olenevalt sellest kas marmor on tekkinud lubjakivist või dolokivist, koosnevad marmorid, kas kaltsiidist või dolomiidist.
 
Teine oluline alaliik on paekivi. Ta on vähem vastupidavam, kui enamik purskekivimeid, kuid vastupidavam kui enamik teisi settekivimeid. Paekivi saab kasutada ehitusmaterjalina, kuid on happelises keskkonnas ilmastiku poolt kergesti lagundatav, sest vihmavesi, teekonnal läbi õhu, korjab endaga kaasa väikese koguse süsinikdioksiidi ja see muudab vihma nõrgalt happeliseks. Kaltsiit aga on happe vastu kaitsetu.
 
Eesti rannikul kohtab tihti ka kivirahnusid ehk rändkive millest kuni 65% võib koosneda settekivimitest, mis on mandriliustik siia kandunud umbes 10 - 12 000 aastat tagasi, praegustelt Soome ja Norra aladelt.
 
(EN) To log this eartcache you have to do the following:
 
1) Read the text about limestones in description.
 
2) Please, answer two questions:
 
a) Estimate, how wide is the limestone coast near given coordinates.
 
b) What are the colours of limestones on this coast?
 
Please, do not post the answers on this site, but send them to me and log the cache, do not wait for my approval.I will contact you only in case of problems!
 
3) This point is optional! Build the stone pile (size is up to you). Take two photos. First one should represent the building process. The other one should contain you, your GPS and your finished stone-pile. Attach your photos to your log.
 
(EST) Earthcache logimiseks pead tegema järgmist:
 
1) Loe tutvustavat teksti lubjakivist aarde kirjelduses.
 
2) Palun vasta kahele küsimusele:
a) Kui lai on lubjakividest koosnev pangajärsak antud koordinaatide lähedal.
b) Mis värvi on lubjakivi sellel rannikul?
 
Palun ära postita vastust sellele lehele, vaid saada see mulle ja oota minu nõusolekut logimiseks.
 
3) See punkt on vabatahtlik! Ehita kivikuhilake (suurus sõltub sinu fantaasiast). Tee kaks fotot. Esimene peaks kajastama ehitusprotsessi. Teisel peaksid olema sina, sinu GPS ja sinu valmisehitatud kivikuhilake. Lisa fotod oma logile.
 
Have fun!
 
Naudi!

Additional Hints (Decrypt)

Lbh ner serr gb ybt guvf pnpur nsgre lbh unir frag gur nafjref gb zl dhrfgvbaf! V jvyy pbagnpg lbh bayl va pnfr bs ceboyrzf!

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)



 

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