Please note that this is an Earthcache; a find will only be accepted if the Logging Requirements have been met.
Solnhofen Limestone from Bavaria
Ground zero is at the Withy Grove entrance to the Arndale Centre. Many of the walls in the centre are clad with polished limestone quarried in Bavaria and called Solenhofen Limestone. This attractive 150 million years old Jurassic limestone is renowned for its preserved soft bodied animals including Archaeopteryx. (This EarthCache has a far less exotic objective)
The limestone was deposited in the Mesozoic era-which is comprised of Triassic, Jurassic, and Cretaceous periods in geological time. Triassic rocks can be seen most clearly alongside the M60 in Stockport, but Jurassic and Cretaceous are not present in the area, where at that time it was dry land. So to see Jurassic or Cretaceous rocks a visit to the Yorkshire coast or the south coast from Dorset eastwards to the well known Cretaceous 'White Cliffs of Dover' will be required. A glimpse of the Mesozoic can be had in the Arndale centre without getting wet!
The majority of fossils preserved in the Solnhofen Limestone are of marine origin, but the most famous of its fossils discovered about 1850 is the amazing Archaeopteryx
Already we had been confronted with an array of unusual words coined by 19th Century geologists to identify and subdivide the rocks of this country, so they can be compared with those in other parts of the world. So how does this work? How do we know the relative ages of rocks? We learn from a quite tender age that dinosaurs roamed through 'Jurassic ParK' having first appeared in the Triassic period and becoming extinct at the end of the Cretaceous. So if we find a fossil dinosaur it is Mesozoic! Sadly we don't bump into dinosaur bones very often, but Ammonites on the other hand are quite common. They existed throughout the Mesozoic before disappearing with the dinosaurs at the end of the Cretaceous. So what is special about Ammonites? They are coiled quite liked Rams' Horns, vary in size from an inch to several feet in diameter, have been known for thousands of years, and in folk lore they are called in places ''Snakestones'; they are easily recognised. Why else are they better than dinosaurs for ageing rocks? As they mature Molluscs grow in size and they need a larger living space. Unlike Hermit Crabs which move into larger shells as they grow, Ammonites were like snails and grew their own shells. A line showing where the old living area ended and the new, larger area begins, is visible on the outer surface of a fossil Ammonite and is called a Suture line. These Suture lines varied in shape from species to species, generally becoming more complex throughout the Mesozoic era. This variation led to Ammonites being adopted as Zone Fossils. Some creatures remained constant in structure over millions of years and were useless as Zone Fossils. Ammonites evolved over the Mesozoic, so finding a particular fossil in different locations indicates that the rocks in those locations were deposited in the sea at more or less the same time. The Zone Fossils are thus geological calendars. If we could identify the Ammonites in the Arndale Centre, we could age the Stolnhofen Limestone without going to Bavaria.
1. For the benefit of the CO who suffers from Daltonism what colour is the Stolnhofen Limestone?
2. Find a fossil Ammonite (good for the kids)and state its approx diameter.
3. Remember that the polished rock sometimes cuts a section through an Ammonite. Find an example and describe the shape of the cross section of the chamber.
4. Could dinosaurs be suitable Zone Fossils and if so why?
5> (Optional) Take a photograph of yourself with a fossil Archaeopteryx.
This EarthCache is carried out at your own risk. The CO will not accept responsibility for any expense incurred in this area!