Gram Lergrav - Gram Clay Pit EarthCache
Gram Lergrav - Gram Clay Pit
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Gram lergrav blev tidligere anvendt til teglstensproduktion. I dag er det et museum, der viser Danmarks mest komplette samling af fossiler fra Gram lergrav – Gram Formationen.
Vær opmærksom på, at denne EarthCache kun kan logges i museets åbningstid. Det er valgt, fordi den åbne lergrav alene ikke vil kunne opfylde kravet til Earth Science lessons. Til gengæld vil besøg i lergraven kombineret med besøg i udstillingen bibringe en unik mulighed for at lære om og vise fossiler i Danmark.
Entre i 2012 på 30 kroner (4,50 euro), gratis for unge under 18 år og fri parkering. Selve lergraven er altid tilgængelig.
1. maj - 31. august:
Åben alle ugens dage kl. 10.00 - 17.00
1. september - 30. april:
Åben alle ugens dage kl. 13.00 - 16.00
24., 25., 31. december og 1. januar er der lukket.
Mest betydningsfuldt i udstillingen er samlingen af talrige hvalskeletdele og et enkelt næsten komplet hvalfossil. I lergraven er det muligt selv at komme på fossiljagt i leret med gode chancer for at finde fx fossile snegle og muslingeskaller. Også større ting dukker op. Husk regnbukser og gummistøvler og vær indstillet på at blive snavset.
Denne EarthCache befinder sig i den vestlige del af Sønderjylland lidt nord for Gram. Den vil føre dig nogle millioner år tilbage i tiden til en geologisk periode med et varmt klima og betydelig højere vandstand i havene. Det betød, at stedet dengang lå på bunden af et hav, der var 50 – 100 meter dyb og ca. 30 km ude i havet. I den sene del af perioden har vanddybden været noget mindre. Kontinentaldrift, klimaforandringer, aflejringer m.m. har sidenhen ændret på landskabet, så Gramområdet i dag er fast land. Området ligger vest for sidste istids gletscherkant, så jordens overflade er ikke blevet forstyrret af isens bevægelser hen over landet under de forskellige foregående istider. På bunden af dette hav har der aflejret sig tykke lag af finkornet ler, sandsynligvis fra nedbrydning af det Skandinaviske grundfjeld. Man har målt lerlaget i lergraven til at være 35 meter tykt. Gram Formationen består nederst af ca. 3 m brunt til grønligt glaukonitholdigt ler med få fossiler. Det er et grønligt glimmersand
K (Fe3+,Al,Mg)2(Si,Al)4O10(OH)2 opstået ved en kemisk reaktion i havvand.
Herover et tyndt lag rødbrunt goethitholdigt ler. Et jernmineral (FeO(OH)). Så følger et ca. 25 meter tykt lag brunt Gram Ler, der bliver sort eller gråt, når det forvitrer. Det lag er rigt på fossiler, så det er i dette ler, man går på fossiljagt. Øverste lag i Gram Formationen består mest af finkornet sand.
I perioden hvor leret blev gravet op til produktion af teglsten, dukkede der mange fossiler af havdyr op – fra mikroskopiske små dyr til adskillige hvalfossiler. Især bardehvalfossiler er fundet i leret. Det skyldes nok, at der har været gode betingelser for føde til plankton og småfisk. Fossilerne blev i 2005 samlet i Museum Sønderjylland - Gram lergrav.
Det store antal fundne fossiler er med til at fortælle om den artsrigdom, der var i havet dengang. Hvalerne var måske ikke så store, som dem vi kender i dag. Til gengæld er der fundet en hajtand, der er godt 15 cm lang. Den stammer fra kæmpehajen Carcharocles megalodon, der var mere end dobbelt så stor som de nulevende hajer. Den har vejet op til 60 tons og var 14 meter lang. Halefinnen var 3 meter høj. Dens livret har været små hvaler, delfiner, marsvin og sæler. Megalodon uddør for ca. 1,5 millioner år siden, muligvis fordi jordkloden på det tidspunkt havde fået et så koldt klima, at store dele af Jordens vand var bundet som is. På museet kan du se en model af dens kæber.
Fossiler dannes ved at dyret/planten, efter at de er døde og indlejret i en søbund eller havaflejring, udsættes for en lang række kemiske og fysiske påvirkninger. Porer i skaller og knogler vil ofte blive udfyldt af et mineral (imprægnering eller forstening). Aragonit kan omkrystalisere til calcit og organiske materialer omdannes til kul og grafit. Oprindelige dele kan også blive erstattet med et andet mineral; oftest jernsulfid, kisel eller calciumcarbonat. Alle disse processer foregår under tryk fra det overliggende vand- eller jordlag.
En vigtig forudsætning for fossilbevaring er, at organismen begraves hurtigt efter døden. Hvis dette ikke sker, vil en lang række biologiske og fysiske processer normalt opløse, nedbryde eller sprede selv de mest bestandige skeletdele i løbet af få år. Det kan også blive spist af ådselsædere.
En anden vigtig forudsætning er, at organismen indeholder hårde eller modstandsdygtige bestanddele; bløddele som muskler og hud bevares kun under helt specielle omstændigheder
Du kan finde mere om Gram lergrav og Gram Formationen på (visit link)
For at logge denne EarthCache skal du besvare følgende opgaver i en mail til vica2010 samtidig med du logger på Geocaching.com. Ved korrekte svar accepteres logningen.
a) Fra hvornår til hvornår blev Gram Formationen dannet? Svar i hele mio. år.
b) Hvilken farve har fossiller fra Gram Lergrav og hvorfor?
c) Hvor lang er det længste fossil af en bardehval på udstillingen?
d) Hvor mange arter af snegle er der fundet i leret?
e) Hvorfor finder man tænder og ikke skelletter fra hajer i Gram leret?
f) Hvor mange tænder er der i munden på en Megalodon?
English version:
Short Description:
Earlier Gram Lergrav (Gram Clay Pit) was used for production of tiles. Today it is a museum exhibiting the most complete collections of fossils in Denmark called “The Gram Formation”
Long Description:
Please be aware this cache can only be logged in the opening hours on the museum. A visit to the open clay pit alone will not fulfill my demands for an Earth Science lesson. In return for that, visiting the clay pit combined with visiting the exhibition you will get a unique opportunity learning about and seeing fossils in Denmark.
Admission to the exhibition is free for people under 18 years old.
Adult has to pay 30 dkr. or 4,50 euro.
Parking is free and the clay pit is always open to the public on one’s own responsibility.
Opening hours:
1. May – 31. August
Every day 10.00 – 17.00
1. September – 30 April
Every day 13.00 – 16.00
24., 25., 31., December and 1. January closed.
Most important is the collection of numerous parts of skeletons from whales and one nearly complete whale fossil. In the claypit it is possible to go for a fossil hunt on your own in the clay pit and with good possibility for finding e.g. fossils of snails and shells. Bigger fossils also rise to the surface. Remember waterproof trousers and rubber boots and please be prepared for getting very dirty.
This Earth cache is located in the western side of South Jutland a little north of Gram. It will lead you some million years back in time to a geological period with a warm climate and a high sea level. This caused that the area at that time was on the bottom of an ocean 50 – 100 m deep and about 30 km from the coast. In the late part of this period the water has been less deep. The temperature was falling and more water was bound as ice on the North- and South Pole and the sea level went down. Continental drifting, climate changes, depositing and so on has afterwards changed the landscape, so today the area around Gram is solid land. The area is to the west of the glacial border from the last Ice Age 10.000 years ago, so the surface of the earth has not been disturbed from the ice moving over the country during the periods of Ice Age.
On the bottom of this ocean, sediments have settled in a thick layer of fine-grained clay, probably from erosion of the Scandinavian bedrock. The thickness of the layer of clay is measured to be about 35 m. On the bottom the Gram Formation consists of about 3 m brownish or greenish glauconitic clay with few fossils.
A mineral K (Fe3+,Al,Mg)2(Si,Al)4O10(OH)2
Over this there is a thin layer of ginger goethite clay (FeO(OH)). Then followed by about 25 m thick, brown layer of Gram clay; characteristic by being grey when it disintegrate. This layer has an abundance of fossils. It is in this layer (the grey clay) you can find fossils in the surface of the pit. On the top of the Gram Formation you will find a thin layer of fine-grained sand.
In the period when the clay was used for making tiles a numerous amount of marine fossils were found; from microscopic small animals to quite a few fossils of whales. Because of the good conditions of nourishment for plankton and smaller fish in particular fossils of baleen whale is found in the clay. In 2005 all these fossils was exhibited in the new “Museum South Jutland – Gram clay pit.”
The large number of fossils tells you about the richness of species in the ocean at that time. The whales were not as big as whales known today. On the other hand they have found a tooth over 15 cm long from a shark. It comes from the giant shark Carcharocles Megalodon; twice as big as the living sharks, weight up to 60 metric ton and 14 m long. The tailfin was 3 m high. The favorite dish was small whales, dolphins, porpoises and seals. The Megalodon shark becomes extinct for about 1.5 million years ago. At that time the earth has got a very cold climate; so cold that most of the water on earth was frozen. In the exhibition you can see a model of the Megalodon jaw.
Fossils is created when the dead animal or plant drops to the bottom of the ocean and quickly berried in the mud. Here the organism is put to a serial of chemical and physical influence. Pores in shells and bones will often be filled with a mineral (fossilization). Aragonite can re-crystallize into calcite and organic material is transformed into carbon and graphite. Original parts can also be replaced by another mineral; often iron sulfide (FeS), kiesel or calcium carbonate. All these processes take place under pressure from the overlying layer of water and/or sediment.
An important condition for fossilization is that the organism is quickly buried after the death. If not, a serial of biological and physical processes normally bring the organism in a state of decomposition, even the skeleton, within a few year. Soft parts such as muscles and skin is only preserved under very special circumstance .
You can read more about Gram Clay Pit exhibition and the Gram Formation on www.museum-sonderjylland.dk/naturhistorien.html
If you want to log this EarthCache you have to answer the following question send by mail to vica2010 when you are logging on www.geocaching.com. If your answers are correct your logging will be accepted.
a) From when till when was the Gram Formation formed? You may answer in whole million years.
b) What is the colour of fossils from the claypit and why?
c) How long is the longest fossil of an barleen whale in the exhibition?
d) How many species of snails is found in the clay?
e) Why is it, that you can find teeth and not skeletons from sharks in the clay pit?
f) How many teeth are there in the Megalodon jaw?
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