Day at the Geology Department – Cardiff Museum
Posted: October 21, 2014 Filed under: Subject | Tags: Nation Museum Cardiff, sedimentary rock, Volcanic ash
Shale bored by Pholas
Pholas shells still inside the holes
Close up of a pholas shell.
Ripple structure – formed in shallow sea, when exposed to the weather sea levels lowered, then the rock was exposed to sun and cracks formed.
Sun cracks in rocks.
Close up of sun crack in the rock
Clay Ironstone. Septarian Concretion
Close up of the pattern.
Volcanic Ash which accumulated on the sea floor and entombed some of the animals living there. These are the shells of the brachiopod Orthis.
A rock resembling a tooth or a medieval tool. Many rocks have legends surrounding them because of their shapes but this was formed entirely naturally as acid rain eroded the limestone rock.
Rock Pigeon – Do you believe this is an entirely natural sedimentation of rock?
The movement of a fish preserved in stone. The fish’s pathway has been preserved for millions of years – not the body, but the movement – look at movement on my rocks. The fossil shows not only the fish’s path but also a trace of a centipede with 6 legs and a creature with fins/spikes that when they rested made a mark.
Fossilised imprint (Graplolites)- extinct fine 2D coral – intricate, detailed network, mesh. 100’s of minute animals living off it, linked as a colony.
Large chalk rock with holes.This rock was large enough to get a better view inside the holes. I need to collect more larger versions of these rocks.
A view inside a hole in a piece of chalk rock from sussex. The hole was made by a bivalve mollusc and you can see in this picture that the shell of the creature remains stuck inside. This creature bores into the rock by grinding it with its gastropod. (abrasive mouth parts) The shell forms a cross hatch pattern of ridges as it turns, it grinds the soft chalk down.
Magnifying glass to get a better view of inside the holes.
The chalk rock is cretacious however the borings are modern. We can tell this because of the modern shells left inside.
here’s one of them
Lots of smaller holes, possibly made by sponges. They get nutrients from minerals inside the rock when they dissolving the rock.
To get a perspective of size, here is the large chalk rock alongside some of my rocks.
A thick ammonite. I have never seen an ammonite like this before. It likely rolled along the sea bed rather than swam.
Earscene? wood which is 50 million years old. Bilvalves bored into the wood and the holes lined with calzine crystals as the water crytalized over time.
All objects photographed are courtesy of the Nation Museum Cardiff.
Other info I learnt:
XRD scan – tells you what minerals are in a rock.
They still use the Old County system in the Geology archive.
Ripple structures and sun cracks that I was shown were over 2 million years old.
Go to Lavenock – could find some rocks with holes there.
Look up Glaglomerates, brachiopods, bivalves, pholas (mollusc), Cliona (sponge), grapholites
Volcanic ash deposits – built in layers. layers in volcanic as well as sedimentary rock. they collect contemporary material. eg ash from the recent ash cloud. Volcanic oddities – volcanic bomb, spindle bombs for tourists. lava medallions and coins in lava sold as souvenirs.
Cave pearls grow in pools within caves. They are built in layers like a pearl or an oyster. Grown around dirt and deposits.
Coal collection – irreplaceable – the mines have now closed/flooded so no coal like this can be retrieved now.
At Southerndown there is Carveniverous rocks and Triassic rocks in layers. There is a huge gap in time between the layers. This is called an un-conformity.
Brachiopods – look into these creatures and the differences between them and bivalves. http://livelikedirt.blogspot.co.uk/2009/11/sunday-inverts-bivalvia-vs-brachipoda.html
South Wales Geological Association – downloads for walks
Penarth – silocerous – contain the earliest ammonite.
Ammonites come in many different shapes caused by water type, tides, climate etc
- Tell the story of the bivalve mollusc in the rock.
- Make the paintings more accurate? Paint directly from viewing these rocks.
- Projecting onto rocks