Fossilization (Basic Taphonomy)

  1. Two broadly recognized types of fossils
    • Body fossils - remains of the organism itself
    • Trace fossils - evidence of the movement or activity of the organism - track trail or burrow.
  2. Requirements for preservation of fossils.
    1. Generally, Hard parts, or Skeletons are required.
      • Calcite (CaCO3): molluscs, coral, some sponges, foraminifera,
      • Silica (SiO2): some sponges, radiolarians, diatoms, parts of some plants
      • Hydroxyapatite (Ca5(PO4)3(OH)): Vertebrate bones teeth and fish scales.
    2. Environmental factors in the preservation of fossils
      1. Oxygen
        • Encourages scavengers and growth of microbes which break down rock
        • Reacts directly with tissues to break them down
      2. Movement
        • Tends to disarticulate complex skeletons
        • Can erode or fragment shells and bones
      3. Acidity
      4. Other living things
        • Tend to recycle dead material
        • Create movement
        • Churn sediments, make oxygen more available
      5. Diagenesis: changes in the sediments after burial
    3. Fossils must be buried in sediments, which become sedimentary rocks.
      1. Sedimentary rock types and their preservation potentials
        1. Clastic sedimentary rock types (larger particle sizes deposited by faster current).
          1. Conglomerates.
            • Fossils very rare. Too coarse for preservation of many fossils
            • Larger bones (Dinosaurs)
            • Wood
          2. Sandstone.
            • Fossils not common - subject to flow of water.
            • Excellent preservation of trace fossils
            • Larger shells & skeletons: coarse preservation
          3. Siltstone.
            • Fossils common
            • Excellent preservation of trace fossils
            • Finer Shells & skeletons
          4. Mudstone.
            • Fossils common
            • Sediment compresses dramatically
            • Seals out oxygen
        2. Chemical.
          1. Limestone.
            • Frequently made of fossils (shells): almost always contains them
            • Forms abundantly under normal marine conditions.
            • Solidifies rapidly.
          2. Gypsum (rare fossils - Rocks around Paris)
      2. (Rarely) Igneous rocks will trap animals and entomb them
        1. Ash falls (several examples from great plains of US.
        2. Ash flows
      3. Metamorphic rocks - fossils in originally sedimentary rock survive metamorphism.
      4. Diagenesis - changing sediment into rock
        • Compaction
        • Cementation
        • Recrystallization
  3. Preservation
    1. Original preservation.
      1. Mummification.
        1. Frozen: Mammoths of Siberia
          1. Another Talkorigins debate Catastrophe?
          2. Picture of Dima
        2. dessicated.
    2. Permineralization.
    3. Recrystallization.
    4. Replacement
    5. Molds and cast.
    6. Entombed
      1. Natural History Museum in UK nucleic acids (DNA) from insects in amber
      2. Calpolytech attempts at DNA from amber insects
      3. American Museum of Natural History Amber Exhibit
    7. Carbonization.
  4. Lagerstätten: fossil deposits with exceptional preservation