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Obora Hvezda

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Hidden : 10/10/2010
Difficulty:
1.5 out of 5
Terrain:
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Geocache Description:

Devata zastavka naucne stezky v peknem parku Obora Hvezda, zabyvajici se mistni geologii. Na vychozich souradnicich naleznete informacni ceduli, ktera Vam pomuze s odpovedmi.

At the start coordinates, find information board, which will help you with answers.


[Cesky]

Geologie Obory Hvezda

I kdyz byla obora u letohradku Hvezda vyhlasena za zvlaste chranene uzemi predevsim z lesnickeho a botanickeho hlediska, vyskytuji se tu misty prirozene a misty umele vychozy kridovych hornin. Nejvice vychozu je v jizni a zapadni casti obory, v same blizkosti ohradni zdi. V teto casti obory je tvori predevsim horniny cenomanu, piskovce, jejichz stari se odhaduje priblizne na 100 milionu let.

Ve spodni casti jsou to rezave zlute az zlutosede hrubozrnne kaoliniticke piskovce peruckych vrstev. Obsahuji silnou primes rezaveho vodnateho oxidu zeleziteho - limonitu a o tom, ze vznikaly v neklidnem prostredi nedaleko morskeho brehu, svedci jejich vyrazne krizove zvrstveni. Prave v techto piskovcich se vyskytuje tzv. zvoden - zvodnela vrstva, ktera byla vyuzita jako jimaci misto vody pri stavbe vodovodu pro Prazsky hrad v dobe vlady Rudolfa II.

V nadlozi se uz vyskytuji typicke morske ulozeniny vrstev korycanskych. Spodni hrubozrnne piskovce jsou prekryty razem zlutosedym stredne zrnitym piskovcem, ktery uz vznikal v morskem prostredi, ackoli breh tehdejsiho more nebyl prilis vzdalen. V piskovci se nachazeji stopy po lezeni i nevelka doupata morskych organismu, nejspise mlzu, jejichz neurcitelne zbytky se v piskovci rovnez vyskytuji.

Treti vrstvou, se kterou se v tomto prostoru setkame, jsou nazelenale az tmave zelene, stredne zrnite az jemnozrnne piskovce s glaukonitem. Prave glaukonit, mineral z tridy kremicitanu s dvojmocnym zelezem zelenosede barvy, zbarvuje piskovce do zelena. V piskovcich jsou cetne stopy po lezeni mlzu a pomerne casto se najdou i jejich zkameneliny, hlavne mlzu Protocardia hillana (SOWERBY), Lopha diluviana LAMARCKRhynchostreon suborbiculatum (LAMARCK).

Mlz Protocardia hillana (SOWERBY)
Mlz Protocardia hillana (SOWERBY)
Ustrice Lopha diluviana LAMARCK
Ustrice Lopha diluviana LAMARCK
Ustrice Rhynchostreon suborbiculatum (LAMARCK)
Ustrice Rhynchostreon suborbiculatum (LAMARCK)

Nad touto vrstvou se setkame i s ulomky opuk nejmladsiho souvrstvi, belohorskeho, ktere je v obore Hvezda dobre odkryto v byvalem lomu u samotneho letohradku. Ty byly odkryty okolo lumku vedle letohradku. Opuky belohorskeho souvrstvi byly stavebnim kamenem stredoveke Prahy.

Dnes je to polozarostly lumek a nevznikl v techto mistech nahodou. V minulosti se v nem lamaly opuky patrici ctvrte vrstve naseho profilu, ktere slouzily jako vyborny stavebni kamen, ze ktereho je postavena znacna cast stredoveke Prahy, a byly take pouzity pri stavbe letohradku Hvezda. I dnes se na nekterych mistech u Prahy a Rakovnika tezi, ale slouzi vetsinou pro opravy stredovekych kulturnich pamatek.

Opuka je vzity termin pro piscite slinovce s hojnou primesi oxidu kremiciteho (hlavne ve forme chalcedonu nebo opalu, mene kremene), ktery tvoril hlavne kostry zivocisnych morskych hub (Porifera). Opuky jsou belave az zlute barvy a pri tezbe se z nich vyrabi male kvadry, ktere jsou potom uzivany pri stavbe jako material zdiva.

Behem usazovani opuk belohorskeho souvrstvi doslo k prohloubeni a rozsireni ceskeho kridoveho more. Opuky se usazovaly dale od pobrezi a dosahly v Cechach znacneho rozsireni. Jsou to usazeniny jemnozrnne se silnou prachovou primesi a to je cini pevnymi a odolnymi i stovky let proti neprizni pocasi. Nejen ve Hvezde, ale na Strahove, v Brevnove a v okoli Bile Hory se tezila opuka jako stavebni kamen. Dnes jsou temer vsechny lomy a lumky na opuku zasypane a maly, polozarostly lom u Hvezdy se stal vzacnou raritou.

I v opukach byla nalezena rada zkamenelin dokladajicich zivot v tehdejsim mori. Vyznacni jsou mlzi druhu Mytiloides labiatus (SCHLOTHEIM)Mytiloides hercynicus (PETRASCHEK), dalsi mlzi Lima aspera MANTELL, Spondylus spinosus (SOWERBY) ci Exogyra lateralis REUSS, plzi Leptomaria seriatogranulata (GOLDFUSS), Turritella multistriata REUSS ci Rostellaria reussi GEINITZ, hlavonozci amoniti jako Mammites nodosoides (SCHLOTHEIM) nebo Collignoniceras woollgari (MANTELL). Krome nich se nasly i pozustatky raku, ryb ci zuby zraloku a dokonce i casti celisti a obratle morskeho plaza plesiosaura.

Mlz Mytiloides labiatus (SCHLOTHEIM)
Mlz Mytiloides labiatus (SCHLOTHEIM)
Leptomaria seriatogranulata
Leptomaria seriatogranulata
Amonit Collignoniceras woollgari
Amonit Collignoniceras woollgari
Horni celist velke drave ryby Xiphanticus sp. z Bile Hory
Horni celist velke drave ryby Xiphanticus sp. z Bile Hory

Protoze v minulosti probihala tezba opuk rucne, lepe se pri ni objevovaly zkameneliny. Jejich studiem dnes vime o ceskem kridovem mori mnohe a take mnohe zdejsi zkameneliny jsou dnes vystaveny v Narodnim muzeu v Praze, Ziskal je pro ne profesor paleontologie a kustod paleontologickych sbirek Narodniho muzea Antonin Fric. Ten take sestavil prvni idealni profil belohorskymi a "malnickymi" vrstvami podle poznatku, ktere ziskal z vyzkumu na Bile Hore, u Drinova a Vehlovic. Na profilu tvori belohorske souvrstvi vrstvy 2 az 9, vyssi vrstvy nalezi k prechodnim poloham k souvrstvi jizerskemu.

Profil geologickych vrstev ve Hvezde
Profil geologickych vrstev ve Hvezde
Ulozeni geologickych vrstev v okoli Hvezdy
Ulozeni geologickych vrstev v okoli Hvezdy


Pro uznání logu:
1. pridejte k logu fotku vas a vasi GPSky s pozadim odkryvu. (dobrovolne)
2. vytvorte e-mail z odpovedi na nasledujici otazky:
  • a) jake je odhadovane stari zdejsi opuky z Belohorskeho souvrstvi? (v milionech let)
  • b) v prave horni casti odkryvu se nachazi vyryte jmeno. Kolik ma pismen? (fotohint)
  • c) kolikacipa je ruda (ruska) hvezda? :-)

E-mail bude mit tvar [odpoved a] [odpoved b] [odpoved c] oh@gmail.com. Pouzijte pouze cislovky, bez mezer. (Pro priklad, e-mail bude vypadat jako 4018oh@gmail.com). Telo e-mailu nechte prazdne, do predmetu napiste vasi prezdivku na geocaching.com. Pokud vas e-mail bude mit spravny tvar, obdrzite automatickou odpoved o spravnosti okamzite.

Nedodrzeni podminek muze mit za nasledek smazani logu.

[English]

The Geology of the Game Preserve Hvezda* (Hvezda means "star")

The game reserve located at the summerhouse Hvezda was declared an especially protected territory mainly for forestry and botanic reasons, but also thank to the occasional natural and artificial outcrops of rocks. Most of the outcrops can be found in the southern and western section of the preserve, in the proximity of the preserve wall. Most of the outcrops in this part of the preserve are of sandstone, and there age is estimated at approximately 100 million years.

The reddish yellow and yellow-grey coarse-grained sandstones in the lower part of the location contain a strong admixture of iron, and their origin harks back to the uniquiet enviroment not far from the sea coast. It was in these layers that water was taken for the water supply of the Prague Castle under the rule of Emperor Rudolf II at the beginning of the 1600s.

The overburden is already occurring typical marine sediments layers korycansky. The lower coarse-grained sandstones are overlaid Raz yellow -grey medium-grained sandstone that had originated in the marine environment, although the former sea shore was too far away. The sandstone with traces of the climbing the tiny burrows of marine organisms, possibly molluscs, whose indefinite residues in sandstone also occur. The third layer, which is in the area meet, are greenish brown to dark green, medium-grained and fine-grained sandstone with glauconite. Right glauconite, silicate mineral from the class of bivalent iron greenish color turns to green sandstone. The sandstones are numerous signs of climbing snails and quite often to find their fossils, especially bivalve Protocardia hillana (SOWERBY), Lopha diluviana LAMARCKRhynchostreon suborbiculatum (LAMARCK). (See pictures of the Czech section)

Above this layer is to meet with chips up cretaceous marl youngest strata, Bílá Hora, which is the industry's Star of well discovered in a former quarry in the summer alone. They were discovered about lumku next summer. Argillite Bílá Hora Formation were building blocks of medieval Prague.

Today's halfgrown lumek and in neither of these places by accident. In the past, broke the slate in it belonged to our fourth layer profile, which served as an excellent building stone, which is based on a considerable part of the medieval Prague, and were also used in the construction's Hvezda. Even today in some places in Prague and in Rakovník argument, but are used mostly for repair of medieval cultural monuments.

Argillite is to take a term for the sandy marls with abundant admixture of silica (mainly in the form of chalcedony or opal, quartz currency), which formed a major animal ones skeletons of sponges (Porifera). Argillite are whitish to yellow color and the extraction of them produce small blocks, which are then used in the construction of a wall material.

During sedimentation Bílá Hora cretaceous marl layer formation have increased and enlarge the Czech Cretaceous sea. Marl were deposited farther from the coast and reached a significant increase in Bohemia. They are fine-grained sediments with a strong admixture powder and they are so solid and durable as well as hundreds of years against the weather. Not only the stars but in Strahov, Brevnov in and around the White Mountain was mined spongilite as building blocks. Today, almost all the mines and lumky buried and a small slate, quarry half grown by park has become a rare curiosity.

In board of fossils have been found documenting the life of the former sea. Mussel species are characteristically Mytiloides labiatus (SCHLOTHEIM)Mytiloides hercynicus (PETRASCHEK), another bivalve Lima aspera MANTELL, Spondylus spinosus (SOWERBY) ci Exogyra lateralis REUSS,, snails Leptomaria seriatogranulata (GOLDFUSS), Turritella multistriata REUSS or Rostellaria reussi GEINITZ, cephalopods such as ammonites Mammites nodosoides (SCHLOTHEIM) or Collignoniceras woollgari (MANTELL). Apart from them, they found the remains of the rake, fish or shark teeth, and even parts of the jaw and vertebrae marine plesiosaur reptile. (See pictures of the Czech section)

Because in the past, though the extraction of cretaceous marl conducted manually, the better it appeared fossils. Their study of today know about the Bohemian Cretaceous sea a lot and also many local fossils are now on display at the National Museum in Prague, is earned not a professor and curator of paleontology paleontological collections of the National Museum of Antonin Fric. He also assembled a first ideal profile belohorsky and "malnicky" under layers of knowledge they have acquired from research on White Mountain, and the Drinov Vehlovic. On the side a Belohorsky layer formation layer 2 and 9, finding the upper layer to layer formation in previous positions jizersky. (See pictures of the Czech section)


For the valid „Found It“ log:
1. you have to upload to the log a photo of you with your GPS and the outrop at the coordinates. (optional)
2. create the e-mail adress from the answers to questions:
  • a) what is the estimated age of marlite here? (in millions years)
  • b) in the upper right of the outcrop is located engraved name. How many letters are in this name? (fotohint)
  • c) how many points are on the red star, a symbol of communism? :-)

The adress will be in the form [answer a] [answer b] [answer c] oh@gmail.com. Use the numbers only, no spaces (For the example, the e-mail adress will look like 4018oh@gmail.com). The message body leave unfilled, in the subject line write your GC nick. If your answer will be correct you will receive automatic confirmation message immediately.

If your answer will be incorrect I will contact you for its correction.


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