Leeds Geological Association


Fossils


Related: Local geology  Fossils  The Leeds hippo  Geology and Scenery  Geology and Man 

 


Fossils are the remains or traces of ancient life that have become preserved in sedimentary rocks. They are valuable in that not only do they enable us to see how life has changed through time but they also give an indication as to what ancient environments were like as well as providing a means of dating rocks. Very few organisms become preserved as fossils so the record we have is far from complete. The absence of fossils in a rock does not mean that nothing was living when the sediment was deposited; it is more likely that it just was not preserved. Many different types of fossils from a variety of environments can be found in the Leeds area. What is included here is a very small sample.


Bivalves

 

Bivalves are a group of molluscs that protect their soft bodies by building a shell made of two equal halves (valves). They mostly live in shallow seas but some inhabit fresh water. Wherever they are found they may crawl over or burrow into soft sediment or fix themselves onto solid surfaces. They feed by filtering particles from the water. In the Coal Measures the different forms are useful indicators of marine or fresh water environments.

Carbonicola
Schizodus

Carbonicola - a non-marine bivalve from the Coal Measures.

Schizodus - a bivalve that could tolerate the highly saline Permian seas in which the Magnesian Limestone was deposited.


Goniatites

 

Goniatites were similar to octopus and squids but differ in that they protected themselves with a coiled shell that was divided up into many chambers. The animal only occupied the last chamber and swam using its tentacles or by squirting out water in a form of 'jet propulsion'. As well as providing protection, the shell also acted as a floatation chamber making the Goniatites a highly mobile group of animals. They were widespread in the shallow seas that surrounded, and occasionally flooded, the Carboniferous deltas and coal swamps. They became extinct at the end of the Carboniferous Period.

Gastrioceras

Gastrioceras - a goniatite found in shales of the Millstone Grit


Plant Fossils

 

Plants are rarely preserved complete so it is difficult sometimes to reconstruct the original from the many different types of fragment. All the plants found in the Carboniferous rocks of Yorkshire grew in a hot, wet equatorial climate and were preserved as a result of falling into stagnant swamps where they became buried in mud. Sometimes tree trunks and roots can be found preserved in their positions of growth when they were suddenly buried by an ancient flood.

Calamites
Alethopteris

Calamites stem - a horsetail

Lepidodendron

Lepidodendron - bark pattern

Alethopteris - a seed fern

 



 
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