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WalesGeologyQuick questions
F3: Time and Change
Quick questions on Fossils and biostratigraphy - WJEC A-Level Geology
5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is modes of preservation?Show answer
The common modes are: permineralisation (mineral-rich groundwater fills the pore spaces of a hard part with silica, calcite or pyrite, hardening it); mould and cast (the original hard part dissolves to leave a cavity, a mould, which may be filled to make a cast); replacement (the original material is dissolved and replaced, molecule for molecule, by another mineral); carbonisation (volatile elements are driven off, leaving a thin carbon film, typical of leaves and graptolites); and trace fossils (preserved evidence of activity, such as burrows, tracks and coprolites, rather than the body itself).
What are graptolites in Welsh slates?Show answer
Carbonised graptolites are the classic zone fossils of the Lower Palaeozoic rocks of Wales, their rapid evolution and wide spread allowing fine subdivision of otherwise featureless slates. Ammonites in the Jurassic. Fast-evolving, widespread ammonites zone the Jurassic in great detail and correlate marine rocks across Europe. Trace fossils of environment. Burrow types reveal the energy and oxygenation of an ancient sea floor, adding palaeoenvironmental information that body fossils alone may not give.
What is q1?Show answer
State three conditions that favour the preservation of a fossil. [3 marks]
What is q2?Show answer
Why must a good zone fossil have a short vertical range? [2 marks]
What is q3?Show answer
Explain what correlation means in stratigraphy. [2 marks]
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