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Fossils

Fossils. Introduction. Jane Ladson, 2003. What is a fossil?. The remains of an ancient organism (plant or animal life) OR The trace of the activity of such an organism e.g. coprolites (droppings), trails, burrows. What parts are usually preserved?. The skeleton Bones Shells

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Fossils

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  1. Fossils Introduction Jane Ladson, 2003

  2. What is a fossil? • The remains of an ancient organism (plant or animal life) OR • The trace of the activity of such an organism e.g. coprolites (droppings), trails, burrows

  3. What parts are usually preserved? • The skeleton • Bones • Shells • Protein based skeletons (carbon traces) Note: Occasionally freak conditions occur that allow complete preservation e.g. insects in amber, animals preserved in ice or peat bogs

  4. Modes of Preservation • Actual remains • Hard parts • Petrifaction / mineral replacement • Calcification • Silicification • Pyritization • Moulds and casts Step1 Organism (hard parts) buried in sediment Step 2 Original material dissolves To leave an exact mould of itself Step3 New material infills mould to produce a cast. Both mould and cast are fossils and each shows detail of original organism

  5. Conditions favouring preservation • Areas of deposition • Rapid burial • Tranquil conditions (no current action) • Lack of scavengers • Lack of oxygen

  6. Life and Death Assemblages • Life assemblages – fossils found preserved in living positions • Death assemblages – fossils NOT in living positions • Derived fossils – incorporated into later sediments

  7. Classification of fossils

  8. Why are fossils important? • Help us to understand the theory of evolution • Help us to date and correlate rock sequences • Help us to interpret the environments of the past

  9. Zone Fossils

  10. What is a zone fossil? • Fossils used to divide the geological column into biostratigraphical units (zones) • Fossils that make a zone unique

  11. What makes a good zone fossil? • Wide distribution • Abundant • Short time span (rapid evolution) • Facies independent (found in many geological environments) • Good preservation • Easy identification

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