EESA06 Lecture 8
How are fossils formed?
-shells buried and preserved unaltered (<100 million years)
-cavities filled with silica, calcium carbonate, iron – a process called mineralization
-permineralization (most common)
-die in or near water
-soft parts consumed by bacteria
-sedimentation (fine grained = more detail; chemical makeup of rock = colour)
-more sed’s pile on = pressure = rock
-mineral rich water = changes to the shell
Ammolite – an organic gemstone
-iridescent aragonite with trace elements (Fe, Mn, Al, Ba)
-preserved tracks, trails, burrows, borings
-ichnology – study of trace fossils
-bioturbation – process of disturbing sediment
Fossils as clues to ancient environments
-palaeoecology – study of ancient organisms and their environments
-clues from: fossil types, assemblages, fossil morphology, trace fossils
Crinoid aka. “sea lily”, loose like a mop head on a tall stem made up of rings & plates,
found in the shallow seas.
Fossils and stratigraphy
-how do we use fossils in stratigraphy?
-to establish relative age of rock units, correlate units (rocks that represent the
same time period in different locations)
-what information do we need to do this?
-relative age of rock units
-fossil species present in each unit
-establish time of first and last appearance of each species geologic range
Note: certain species only live in certain time periods
What kinds of fossils are most useful for stratigraphic work?
-assemblages (groups) of species